A/P Module lockup

We had this problem when we had A/P Invoice tracker minimized at the same
time we were entering invoices... no error message, the pc just locks up and
we have to reboot to get out.

Also, did anyone ever have this happen? Our payroll person was in a payroll
group, had finished running checks, had printed the register (which showed
the check numbers correctly) and the "post" selection was greyed out. Going
in to select group it showed "no" under "checks printed". My solution was
to reprint checks on plain paper starting at the original starting check
number. The "post" option then worked. What would cause this?