A error during execution of webpage

Question

Hello,

Whenever i tries to execute my website, it shows following error:-

 

" Could not load file or assembly 'App_Code12042012' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)" 

 

I can not  understand what exactly assemblies are missing.

 

Please tell me what should i do..

 

Thanx in  advance.