<< I'm not sure what you mean by the integrated IDE. All of our accessing of the VSS features is through the ...\VFP98\SCCTEXT.PRG and the stuff built into VFP. Is this what you are talking about? >>
Yes, I believe so.

<< This problem is really weird ... We will not have it for months -- and then it will occur every time we build. And then it will stop! We aren't even sure which of the VCXs it is that causes the problem, although we think that it has always been one that had been updated recently. In the past we have been able to remove the VCX from the project manually, and then re-add it. >>
If you're working in a multi-developer environment could it be possible that someone is accidentally removing the class library by accident - then when another developer performs a "Update Project List" the one class library is being removed. During a build the class library that was dropped is still being referenced and gets brought into the project once again, but since it's read-only you get the "Can not update cursor" error.

Hope this helps.