error: The specified module could not be found. (Exception from HRESULT: 0x8007007E)

Hi,
when I try to compile a web application this is what happens:
Error 35 C:\projects\crm\Default.aspx: ASP.NET runtime error: The specified module could not be found. (Exception from HRESULT: 0x8007007E) C:\projects\CRM\Default.aspx 1 1
I dont have any reference as to what module is missing. I tried Dependency walker but it didn't help.
any ideas
...