Could not load file or assembly 'Microsoft.Office.Server' or one of its dependencies

When I click to open any custom List in SharePoint 2007 root site, I receive this error:

An error occurred during the processing of . Could not load file or assembly 'Microsoft.Office.Server' or one of its dependencies. The system cannot find the file specified. 
Troubleshoot issues with Windows SharePoint Services. 

Similarly, when i try to create a new List, i also get the same error. But when i browse back, I see that list successfully creates.

The assembly 'Microsoft.Office.Server' is there in GAC and in Web.config as well. I googled but i could not find any solution. Let me know if anyone know the solution of this error?