Error: Could not update; currently locked by another session on this machine

Very stange problem. I have 2 forms in a database in a fron-end / back-end scenario. I'm the only one using the database. Form A and Form B. Form A does not allow editing. I have a button (made using the wizard) that opens the same record in Form B for editing. When I change something in a memo field of a CERTAIN record (not all records) in Form B, I'm unable to save the changes and get the error: Could not update; currently locked by another session on this machine

I've done a fair amount of messing around already. Here's what I've done so far:

1. Repaired and compacted both DBs. (didn't help.)
2. Read this post and tried several things (none of which led me to a solution): https://www.experts-exchange.com/questions/21580646/ERROR-Message-Could-not-update-currently-locked-by-another-session-on-this-machine.html?qid=21580646

I've Never seen this before and these forms are NOT doing anything beyond what Access creates with it's Wizards. Everything is generic as can be. No special code, nothing.

Ideas?

Thanks in advance.