Optimizer Problem - URGENT!

I get the following error on every page :

Code: 
Fatal error: Incompatible file format: The encoded file has format ID 2003120701, whereas the Optimizer can read up to 2002062301 in /home/nexus/public_html/search.php on line 0
What did I do wrong ?

How can I solve this ?

Thanks

 

 

 

 

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