hi, Robert !

I have some code using solver as the main tool to operate with, and...
- when excel is the main window application, code finish in (say) 3 seconds
- when excel is running in the background, code takes times 140 of its "normal" time (but NO error at all)

you might want to revise your code for some of the solver options (maxtime, iterations, userfinish, etc.)

hth,
hector.

__ OP __
When running the following Solver code, the error directly below comes up
when I click on another application while Solver is running
(ie - If I go to Internet Explorer while this code is running, after a few seconds, the error below comes up):
"No return or halt function found on macro sheet"
I then click on "OK", with is the only button within the error popup menu
and the code continues, seemingly without any damage being done.

I did some research on this error, but only found an article saying that this error comes up in Excel2000 --
I, however, am using Excel2003. The article instructs that in order "To resolve this problem
obtain the latest service pack for Microsoft Office 2000". Since I'm using Excel2003
I'm assuming that the specific issue causing this error that this article refers to was resolved in Excel2003
and therefore an Excel2003 servicepack wouldn't address the issue I'm encountering -- is this a bad assumption?

Any help is appreciated!