Have you tried:
– disabling Google Gears if you have that running/installed.
– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the default theme to rule out any theme-related problems.
– renaming the plugins folder via FTP
– reading http://wordpress.org/support/topic/279132