I stated experiencing the same thing today with Dreamweaver CS4 on a Win7 Prof OS machine. I moved my Dreamweaver configuration folder from C:\Users\UserProfile\AppData\Roaming\Adobe out of that directory, reopened Dreamweaver so the config file basically recreated itself, and paste function now works.
Granted, I didn't have a bunch of configs/personalizations to Dreamweaver but you can always copy back over pieces of the original configuration folder that you moved until the paste function breaks again.
MODERATOR NOTE: This document describes how to re-create your user Configuration folder, including the folder paths for Windows & Mac OS and multiple versions of Dreamweaver: http://helpx.adobe.com/dreamweaver/kb/restore-preferences-dreamweaver-cs4-cs5.html