Allen,
I have reproduced a record lock between PO-C and AP-C.
It goes like this:
One user is receiving a line item on a po in PO-C and the other is entering an INVOICE on that line item in AP-C.
I left the PO-C user with the line item up, ready to post the receipt and then tried to finish out the AP-C entry.
The error message in AP-C says that a record in file BKAPPO is locked by another user.
Now, I try and post the Receipt, and the error message there says that a record in BKAPPOL is locked by another user.
One application locked the BKAPPO then the BKAPPOL and the other application seems to have locked them in the reverse order (BKAPPOL and then BKAPPO).
I remember this being called a 'deadly embrace'.