We are having problems when attempting to post large vendor invoices paying multiple receipts.

There could be up to a few hundred lines to pay.  When we hit post, the system locks up and gives the message "Program modified by another user."
Then, we have to start all over again.

Does anyone know what causes this, and more importantly, what the fix may be?

We believe there are other postings happening at the same time affecting the same database tables & fields.

Thoughts?