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I have seen this once before with a clean install, and it was due to the database not being able to write to a table because user rights for the /tmp/ folder on the server were incorrect. Can you turn on mysql debug in system admin -> preferences -> general settings and see if there are any errors (they should show up in red)? If it is an error that it can't write to some TYI file (or something like that), then it is a database thing. You might want to check the database integrity then, and consult your hosting provider to see if they changed anything in their setup recently.
I hope this helps!
Herko