Note: If you are an Access Hosted Client using Access Capture, please see the following Get support in Access Capture and reference the title of this article.
The error message here is indicating that for the target Database the UserID in question either does not exist in the target Database or the user does not have permissions to write to the Purchase Ledger.
In anycase you will need to check within Dimensions the list of UserRecords and locate the UserID (or prove it's non-existence) in the database.
Once you have done so, depending on the outcome you will need to either create or fix the User record.
The Access Capture integration will then be able to import transactions from Capture to Dimensions.