parts/asm cannot be retrieved

hi

I am having trouble retrieving data from windchill, followed by the massages bellow :

1. The object with the following key was deleted or inaccessible: "wt.epm.EPMDocument

2. Local cache for source "failedRequest" is having incomplete information for merge

3. Local cache contents need to be synchronized with the workspace

does enyone have en idea what could be the problem and how to fix this?