>>This is not my first app running on the client location. My other apps are .Net 3.5. No problems putting our CR reports in those apps.
>>This app I did in VS2010 using 4.0. Of course, CR was not included, which led me down this long, horrible road. I have been spending all week getting CR to work in my .Net 4.0 app.
>>
>>On the client machine where this is dying, you're saying that on the same machine, someone has been able to run CR reports from .NET 3.5?
>>
>>I'll keep thinking....maybe someone else here has an idea....but something tells me this is something with the environment. (That would possibly explain the error message not being helpful)
>
>Yes, that is correct. I have other 3.5 apps running CR reports.

Did you install the CR redistributable for VS2010 on the client's machine? There's a boostrapper idea here:
http://www.sourcehints.com/articles/creating-crystal-report-bootstrapper-for-vs2010.html

Otherwise, did you install this redististributable on the client's machine? http://www.businessobjects.com/jump/xi/crvs2010/us2_default.asp

(Check for the 64-bit if you need that for your clients - I didn't see you mention 32 or 64 specifically)