Barbara,
We have had a few strange conversion issues as well, coming from 3.71 what we have seen is in one of the modules options file there was a record that was not correct. So the last on we had which stopped at the GL conversion and CI, we found in comparing a company that converted that AP_options had three records, the company that did not convert had a fourth record, we delete the fourth record in 3.71, migrated and converted.