If I assume that the PTC product specification is correct, and MC14 needs .NET Framework 2.0, then I think I understand my problem. I had .NET Framework 2.0, 2.0 SP1 and 2.0 SP2 installed. Microsoft states that each service pack is supposed to uninstall the previous version. They also state that sometimes the 2.0 installation gets messed up and cannot be uninstalled in the normal manner, and when that happens, the next service pack is not properly installed and applications that need 2.0 will not run properly. I was unable to install 2.0, but fixed that with a tool from Microsoft. I have not yet cleaned up 2.0 SP1, but after that is done and I uninstall and reinstall 2.0 SP2 I expect I will be OK. Other people with problems running MC14 can help me out by posting if they have only one SP of 2.0, or more than one as I do. In addition, I would like to know if people are using MC14 on XP Pro with only 3.5, as that would tend to blow holes in the "requirement" from PTC that MC14 needs .NET Framework 2.0. I know of one colleague running MC14 on Vista with only .NET Framework 3.5, and don't yet understand how to reconcile that with PTC's claim that 2.0 is required, but I don't have the same confirmation on XP. Vic Roberts