Found a system getting NTDLL.DLL errors out of the blue. No apparent infections. Some programs worked find and others did not. I used Win Debug to track down what DLL files were being loaded with the program.
1. Get the Windows Debugging Tools
2. Open debugging tools.
3. Set the symbols path: SRV*f:\localsymbols*http://msdl.microsoft.com/download/symbols
4. Click open executable off the file menu and pick the program causing problems.
5. Click Debug and then Go.
6. This will display any modules it load. I found a module that wasn’t being loaded by the same program on another system. Once removed it was fixed.