>>>A customer described to me that sometimes when he starts my VFP 9 application, almost right away the application main windows starts "jumping and shaking" (these are his words). He says that the only way he can stop this is by going to the Task Manager. How can I determine what would cause this problem?
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>>>Any suggestions would be greatly appreciated.
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>>I think, this curstomer of your has virus?
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>Maybe. But how do you show them that this is a virus that would cause this?

Just install your appliction on other machine and show the user that no "jumping and shaking" happens.
I outr contractes we always put a clause that we consider something as a BUG if we can simulate it on OUR computer with the DATA from client. That is because so many SYSADMINs doesn't has an idea from thair job :o)