Thanks for your replies. It turns out that was some
kind of memory resource problem. If we reboot the PC
each night before going home, it works flawlessly.

This apps uses a lot of Automation. I suspect we
are running out of system memory. Throwing RAM into the
machine may or may not help, but it is cheap (and this
PC is somewhat memory constrained) so we're doing that.

Thanks again for your response.