Errors like that usually start happening due to corruption in the Dreamweaver cache file. The easiest thing to do to fix it is:
1) Close Dreamweaver
2) Locate the Cache file. On a Windows 7 machine it will be at:
YOU is your Windows user name and
X is the version of Creative Suite being used.
3) In that folder there is a file named
WinFileCache-XXXXXXX.dat. Delete that file and restart Dreamweaver.
If for some reason that doesn't fix the problem, there are other steps that can be taken.
Alternate 1: After closing Dreamweaver, open the Extension Manager and disable all extensions for Dreamweaver. Then follow the steps above.
Alternate 2: Close Dreamweaver and then delete the configuration folder. Dreamweaver will rebuild it using default settings the next time you open the program.