found this info for XP
Dreamweaver CS5.5: C:\Documents and Settings\Your User Name\Application Data\Adobe\Dreamweaver CS5.5\[language]\Configuration
I followed this and deleted the WinFileCache file...RE-booted and file still shows up everytime!! ARG!
Every time I open a page in DW the error pos up....
Every time you restart DW, it'll create a new file cache although the name will be different. That's why I asked if you looked BEFORE or AFTER starting DW after a reboot. Are you sure you are deleting the file that is in the correct location?
I have exactly the same problem and error message even though my setup is slightly different (- Win7Ult, 64 bit, CS6). I've tried deleting the WinFileCache in User\AppData\Roaming\Adobe\DeamweaverCS6\en_US\Configuration and rebooted, whatever, but still get the error saying onOpen is not defined.
I just wondered if you'd subsequently found a solution please?