Could you please provide us with the Sitefinity.log file? We will also require a time stamp from the windows/server event logs, in order to check if the last error in Sitefinity is related to this one.
Also, do you get this error when you log into the administration, or see a navigation control for example? I have a clue, but I am not sure from these details.
You might try to run the following script again your database:
|select * from sf_PageBase where ParentID = NULL
If the result is more than 0 (1, 2... etc) then you are right, there is a recursion. You might fix it by running:
|ParentID = NULL
|ID = ParentID
More information on this exact problem could be found in the following post: http://www.sitefinity.com/support/forums/support-forum-thread/b1043S-bdekgd.aspx
Let me know about these details though.
the Telerik team