I use the CFormsII Wordpress plug-in by Delicious Days on several blogs and have had a bug / error appear on several of them. When in the page editor; CformsII provides a button to allow you to add a form to the page , when not properly installed this button shows an error. Here is how I corrected that error:

1. Deactivate the plug-in in Wordpress
2. Go to your server and change the permissions to the CFormsII folder to 777 ( how do I change permissions? - UNIX – Windows)
3. Reactivate the plug-in making sure to use the “activate” link and not the check-box.

This fixed the problem for me , I hope it helps you.