More info on the background...
We moved all CAD Documents in "Product A" to "Product B", then I deleted all team members from "Product A" and renamed "Product A" to 're-use me".
"user 1" had a workspace associated with "Product A" ("re-use me"). Since he isn't a member of "re-use me", Pro/Engineer tells him that he doesn't have access to that workspace any more.
He is a member of "Product B", so he still has access to the context where all of his CAD Documents are located, it's just that he can't access his Pro/Engineer workspace any more. We assume that the workspace still exists somewhere since you can't delete a product.