Obviously the first thing to check is the respective currencies in AP and GL (the company profile screen). If they are different, this is a serious issue, let us know.
If they are the same, then it is likely the file that contains the AP transactions to be retrieved is corrupted. Try printing it - you will probably have to then key the entries directly into the GL and it is easier to key from the report than from any other printout (however it may not print legibly). Then move or rename the file APGLBTCH.xxx (where xxx is your data extension).
Then post a small AP batch and immediately try retrieving into GL. If it is OK, then you can chalk the incident up to a one-time glitch.