We have a site on our portal having access issue. When the portal admin is not
connected to the site, users who are not in portal admin group can not connect
to the site, and they are getting File Not Found error. As soon as the portal
admin connects to the site, the issue is gone.

The event log gives some details information:
A runtime exception was detected. Details follow.
Message: Cannot insert duplicate key row in object 'dbo.UserMemberships' with
unique index 'CX_UserMemberships_RecordId_MemberGroupId_SID'.
The statement has been terminated.

Does anyone have the same experience? Can anyone provide some advices on how to
troubleshoot this issue?