I would guess you re posting to a General Ledger Account with a Mandatory dimension, which is missing. Try to check the settings for the ledger accounts you are posting to. You can also delete the lines and resubmit those lines.
And some times users do not metion the dimensions because it was not made mandatory for Interim accounts but was made mandatory for Direct unit cost, or the accounts which are being posted at the time of invoicing. I would suggest to see this as well.