Since nobody else can reproduce that problem, either, I suggest you tell them to make changes in batches of the same kind.

Can you replicate it on a different database after you found out both change and combine need to happen in order for this error to occur?

 It works fine on Pervasive in our office.  I have not installed another database platform at their office.  Since we did not do the inital install, we're wondering if it is some sort of program corruption.  We have plans to upgrade to 5.5, so we're going to start over again and see if that straightens it out.  Like Jay says, he hasn't seen anyone have this issue - and it's quite a specific issue (2 or more changes and combines in one change list), maybe it'll right itself after the new install.   Thanks Jay and Kurt for your input.