Steven Zahm@ Matt
It seems your test user account already had a linked entry but that linked entry seems to not have existed or perhaps deleted? When a user or entry is deleted that link should be removed too. In this case it was not. I see that this happens sometimes when users are testing but I have never been able to replicate it. If you let me know the steps you took in order to get this error that could help me track down the issue.
I wonder if the issue is s2Member, there is known issue with it when it has updates, it resets the WordPress roles and capabilities which wreak havoc on plugins which require them like Connections.
Perhaps it too interferes with plugins which hook into the WordPress user delete functions. If it does, then perhaps, the link can not be deleted like it should be causing orphan links.
Is this test user the only one where you had this issue, or are there other?