This was an interesting issue I ran into today. We've got a utility I wrote which can search Outlook MSG files from a desktop interface. As part of the program you can print the results to a PDF - I'm using Crystal Reports to do the printing. We had this application installed on a desktop machine for a while but decided to move it over to one of our servers which had a lot more hard drive space. After moving it, when we attempted to print we'd get the error:

"An error has occurred while attempting to load the Crystal Reports runtime"

At first I thought it might be related to needing the CR DLL's installed instead of just being deployed in the app's directory. We installed them and tried again - same exception. Further down in the error (which was actually helpful - imagine that!), "Please install the appropriate Crystal Reports redistributable (snip) containing the correct version of the Crystal Reports runtime (x86, x64, or Itanium).

Hmm...x86 vs x64 - that has to be it - this was Windows 2003 Server (64 bit) vs. XP. I actually just recently listened to a DotNetRocks podcast which talked about .NET applications running under a 64 bit OS. They mentioned that, by default, most .NET applications are compiled under "Any CPU". That means the code get's JIT'ed to 64 bit code under a 64 bit OS - sounds OK. The only catch is that all the components must also be compiled the same way, otherwise you run into problems. I didn't really want to have two different sets of DLL's so I went back into my application and changed it from "Any CPU" to x86 code and recompiled. Order was restored to the universe.

Links:

http://www.dotnetrocks.com