Problems creating Crystal Reports object on some PCs

We have an application written in VB6 that is calling a VB.NET DLL (part of Visual Studio 2008.) The development box is running Crystal Reports 2008 full version (12.0.2.290), and the clients all have the Crystal Reports 2008 Runtime SP3 installed. We have about 80 companies running this without a problem.

We have 1 company that has about 8 PCs running Windows XP (we have a few other clients running this.) 2 of the PCs work fine, and the other 6 can't create the Crystal Reports object, so we get a VB6 error 91. We were wondering if it was an issue with a conflicting version of another Crystal Reports runtime, but we do have that at other clients, the 2 working PCs are using a Crystal Reports 11 runtime, and we also uninstalled both Crystal Reports runtime (2008 and 11) on 1 PC, rebooted, and reinstalled the CR 2008 Runtime SP3. (We have tried this a few times, and have even logged into do the reinstall as the domain administrator, to no avail.)

It seems odd that there would be 6 PCs at one site that are this obstinate when we have so many other installs running this.

Any suggestions on what to check? We would prefer not to rebuild the problem PCs, but we are kind of at the end of our rope.