If you experience difficulties uploading your workshop item, you will get a return result number from steam in the console. this indicates the reason for the failure, match the number to the items in the following list to help you determine what the issue is:
k_EResultOK = 1, // success
k_EResultFail = 2, // generic failure
k_EResultNoConnection = 3, // no/failed network connection
// k_EResultNoConnectionRetry = 4, // OBSOLETE - removed
k_EResultInvalidPassword = 5, // password/ticket is invalid
k_EResultLoggedInElsewhere = 6, // same user logged in elsewhere
k_EResultInvalidProtocolVer = 7, // protocol version is incorrect
k_EResultInvalidParam = 8, // a parameter is incorrect
k_EResultFileNotFound = 9, // file was not found
k_EResultBusy = 10, // called method busy - action not taken
k_EResultInvalidState = 11, // called object was in an invalid state
k_EResultInvalidName = 12, // name is invalid
k_EResultInvalidEmail = 13, // email is invalid
k_EResultDuplicateName = 14, // name is not unique
k_EResultAccessDenied = 15, // access is denied
k_EResultTimeout = 16, // operation timed out
k_EResultBanned = 17, // VAC2 banned
k_EResultAccountNotFound = 18, // account not found
k_EResultInvalidSteamID = 19, // steamID is invalid
k_EResultServiceUnavailable = 20, // The requested service is currently unavailable
k_EResultNotLoggedOn = 21, // The user is not logged on
k_EResultPending = 22, // Request is pending (may be in process, or waiting on third party)
k_EResultEncryptionFailure = 23, // Encryption or Decryption failed
k_EResultInsufficientPrivilege = 24, // Insufficient privilege
k_EResultLimitExceeded = 25, // Too much of a good thing (most likely preview image is too large MUST BE < 1 Megabyte!)
k_EResultRevoked = 26, // Access has been revoked (used for revoked guest passes)
k_EResultExpired = 27, // License/Guest pass the user is trying to access is expired
k_EResultAlreadyRedeemed = 28, // Guest pass has already been redeemed by account, cannot be acked again
k_EResultDuplicateRequest = 29, // The request is a duplicate and the action has already occurred in the past, ignored this time
k_EResultAlreadyOwned = 30, // All the games in this guest pass redemption request are already owned by the user
k_EResultIPNotFound = 31, // IP address not found
k_EResultPersistFailed = 32, // failed to write change to the data store
k_EResultLockingFailed = 33, // failed to acquire access lock for this operation
k_EResultLogonSessionReplaced = 34,
k_EResultConnectFailed = 35,
k_EResultHandshakeFailed = 36,
k_EResultIOFailure = 37,
k_EResultRemoteDisconnect = 38,
k_EResultShoppingCartNotFound = 39, // failed to find the shopping cart requested
k_EResultBlocked = 40, // a user didn't allow it
k_EResultIgnored = 41, // target is ignoring sender
k_EResultNoMatch = 42, // nothing matching the request found
k_EResultAccountDisabled = 43,
k_EResultServiceReadOnly = 44, // this service is not accepting content changes right now
k_EResultAccountNotFeatured = 45, // account doesn't have value, so this feature isn't available
k_EResultAdministratorOK = 46, // allowed to take this action, but only because requester is admin
k_EResultContentVersion = 47, // A Version mismatch in content transmitted within the Steam protocol.
k_EResultTryAnotherCM = 48, // The current CM can't service the user making a request, user should try another.
k_EResultPasswordRequiredToKickSession = 49,// You are already logged in elsewhere, this cached credential login has failed.
k_EResultAlreadyLoggedInElsewhere = 50, // You are already logged in elsewhere, you must wait
k_EResultSuspended = 51, // Long running operation (content download) suspended/paused
k_EResultCancelled = 52, // Operation canceled (typically by user: content download)
k_EResultDataCorruption = 53, // Operation canceled because data is ill formed or unrecoverable
k_EResultDiskFull = 54, // Operation canceled - not enough disk space.
k_EResultRemoteCallFailed = 55, // an remote call or IPC call failed
k_EResultPasswordUnset = 56, // Password could not be verified as it's unset server side
k_EResultExternalAccountUnlinked = 57, // External account (PSN, Facebook...) is not linked to a Steam account
k_EResultPSNTicketInvalid = 58, // PSN ticket was invalid
k_EResultExternalAccountAlreadyLinked = 59, // External account (PSN, Facebook...) is already linked to some other account, must explicitly request to replace/delete the link first
k_EResultRemoteFileConflict = 60, // The sync cannot resume due to a conflict between the local and remote files
k_EResultIllegalPassword = 61, // The requested new password is not legal
k_EResultSameAsPreviousValue = 62, // new value is the same as the old ( secret question and answer )
k_EResultAccountLogonDenied = 63, // account login denied due to 2nd factor authentication failure
k_EResultCannotUseOldPassword = 64, // The requested new password is not legal
k_EResultInvalidLoginAuthCode = 65, // account login denied due to auth code invalid
k_EResultAccountLogonDeniedNoMail = 66, // account login denied due to 2nd factor auth failure - and no mail has been sent
k_EResultHardwareNotCapableOfIPT = 67, //
k_EResultIPTInitError = 68, //
k_EResultParentalControlRestricted = 69, // operation failed due to parental control restrictions for current user
k_EResultFacebookQueryError = 70, // Facebook error
k_EResultExpiredLoginAuthCode = 71, // account login denied due to auth code expired
k_EResultIPLoginRestrictionFailed = 72,
k_EResultAccountLockedDown = 73,
k_EResultAccountLogonDeniedVerifiedEmailRequired = 74,
k_EResultNoMatchingURL = 75,
k_EResultBadResponse = 76, // parse failure, missing field, etc.
k_EResultRequirePasswordReEntry = 77, // The user cannot complete the action until they re-enter their password
k_EResultValueOutOfRange = 78, // the value entered is outside the acceptable range
k_EResultUnexpectedError = 79, // something happened that we didn't expect to ever happen
k_EResultDisabled = 80, // The requested service has been configured to be unavailable
k_EResultInvalidCEGSubmission = 81, // The set of files submitted to the CEG server are not valid !
k_EResultRestrictedDevice = 82, // The device being used is not allowed to perform this action
k_EResultRegionLocked = 83, // The action could not be complete because it is region restricted
k_EResultRateLimitExceeded = 84, // Temporary rate limit exceeded, try again later, different from k_EResultLimitExceeded which may be permanent
k_EResultAccountLoginDeniedNeedTwoFactor = 85, // Need two-factor code to login
k_EResultItemDeleted = 86, // The thing we're trying to access has been deleted
k_EResultAccountLoginDeniedThrottle = 87, // login attempt failed, try to throttle response to possible attacker
k_EResultTwoFactorCodeMismatch = 88, // two factor code mismatch
k_EResultTwoFactorActivationCodeMismatch = 89, // activation code for two-factor didn't match
k_EResultAccountAssociatedToMultiplePartners = 90, // account has been associated with multiple partners
k_EResultNotModified = 91, // data not modified
k_EResultNoMobileDevice = 92, // the account does not have a mobile device associated with it
k_EResultTimeNotSynced = 93, // the time presented is out of range or tolerance
k_EResultSmsCodeFailed = 94, // SMS code failure (no match, none pending, etc.)
k_EResultAccountLimitExceeded = 95, // Too many accounts access this resource
k_EResultAccountActivityLimitExceeded = 96, // Too many changes to this account
k_EResultPhoneActivityLimitExceeded = 97, // Too many changes to this phone
k_EResultRefundToWallet = 98, // Cannot refund to payment method, must use wallet