Piwik throws error message (Zend)

Just tried to log into my Piwik and I get the following error message:

Fatal error: spl_autoload() [function.spl-autoload]: Class Zend_Log_Exception could not be loaded in /home/myuser/mysite.com/statistics/libs/Zend/Log/Writer/Stream.php on line 132

A couple of hours ago everything worked fine and I haven’t touched or modified anything!

Any ideas what happened or how I could solve this?

TNX

Well I´m not sure what caused the problem, but I solved it by uploading the “themes” folder again to the Piwik location!
Maybe this helps if somebody has the same problem with Piwik 1.0

Regards