When working with IIS7 and Server 2008, and received this message: " is not a valid Win32 application. (Exception from HRESULT: 0x800700C1)"
The problem seems to be that the assemblies used to compile the website are 32 bit assemblies, and need to be "enabled" in the application pool.
1. Open Internet Information Services IIS Manager
2. Select "Application Pools"
2. Locate the application pool for your web site
3. Choose "Advanced Settings..." for the application pool
4. Under the "(General)" section, set "Enable 32-Bit Applications" to True.