MDL Decompiler Error saying "vstdlib.dll was not found."

I recently moved my Steam Folder to my D drive to make more space. Now that I moved it, MDL Decompiler doesn’t work anymore. Some of the tutorials said I have to move a Source SDK File to a certain location. What is this file exactly, where can it be found and where do I put it, I already have Source SDK installed. Please help. Read all the posts one of them has to work.