Hi guys; I'm writing Excel UDF's for clients and publication. I'm finding problems with software running in some versions and different compilation (32 bit or 64 bit). Has anyone thought of or done side by side installation of Office 2007 through 2015 in 32 and 64 bit? Should I run each in a virtual machine or can they co-exist nicely? I would write regression tests in each version and automate release validation. It is done with browsers: you can get a screen with lots of different browsers running the same website and see what goes wrong.