Can I just check that you have tried (with Dreamweaver closed) deleting the WinFileCache file?
If not, delete the file at:
C:\Users\Your User Name\AppData\Roaming\Adobe\Dreamweaver CS5\en_US\Configuration\WinFileCache-XXXXXXXXX.dat (where XXXXXXXXX is some alpha-numeric characters)
Delete the file, and then re-open Dreamweaver and try again. You may have already tried this, but it would be remiss not to check . . .