That's an easy one, you need to turn on automatic versioning so your EXE's have incrementing version numbers. And in the short term, they can delete the old one before they install.

>We have a customer trying to install a new build of an EXE we compiled, in a directory where there is an older build. According to the customer, the older EXE is not being replaced. What could cause this? I've already told my Customer Support guys to check whether the file is marked Read-Only. Is there something in the operating system that might prevent this?