I've seen this before (in our case) when trying to import an archive. And it's ugly. The archive fails midway through import but through adminUI, the server stil thinks the artifacts were imported. No matter what you do, you cannot reimport that archive unless you rename the archive / components. If you try to delete the archive, you get "archive doesn't exist", and if you try to reimport it, you get a message stating that the components already exist.
In our case, it was a problem with our DB2 server - DB Connections were not closing. So somehow communication between LC on websphere and the DB2 server was getting interrupted. I believe our database engineer had to implement some way to close the db connections on a schedule, not sure. But at least that was the root cause of our problem, and it sounds like you may be experiencing the same thing.
