Version Mismatch: Using a 32-bit DLL on a 64-bit installation, or vice versa.
Identify the Architecture: Determine if you are running the 32-bit or 64-bit version of Illustrator CS5.1. Placing the wrong version of amtlib.dll into the application folder will cause a "0xc000007b" error.
Registry Corruption: Windows registry entries pointing to the DLL become invalid. Troubleshooting and Installation Steps