@LarryBradford, it sounds like a required column is not getting populated.
I tend to reverse engineer imports that get ornery by manually entering the transaction I want to import. I then use VI to export the entry into a text file and see how it compares to the file I am trying to import. I then try to use the exported data in an import, defining every column with data, to prove that the process works. It if does, it's now just matter of finding what is in the file that you didn't have and finding the missing data elements required.
I know it sounds basic but sometimes, reverse engineering is easier than banging my head.
With transaction entries the required columns vary depending upon the type of entry entered. (Just like in the data entry screen.)