Error Occurred While Starting Vegas Pro

Hi, everyone! I am in need of serious help! I started using Sony Vegas Pro 9 recently, and it has been working fine until today.
When I opened it up it and got this error message:

Vegas Pro Error
An error occurred starting Vegas Pro.
The TWAIN manager could not be initialized. TWAIN_32.dll missing or corrupt.
I tried downloading Twain_32.dll. It still does the same thing. Any ideas as to how to fix this will be much appreciated!
