Could not load file or assembly 'Microsoft.SharePoint.ApplicationPages.Administration, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. The system cannot find the file specified.

I´ve upgraded Sharepoint 2007 to 2010 and now I get this error in the central administration 

Could not load file or assembly 'Microsoft.SharePoint.ApplicationPages.Administration, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. The system cannot find the file specified. 

How can I fix it ? Any one can help ?

Note,

I upgraded from sharepoint 2007 but in was installed in Windows  server 2003 (x86, 32-bit)