Close, then re-open Paint.NET.
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Look here:
Utilities > View Plugin Load Errors
If any error reports are present, pls. post them.
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Also, open your Paint.NET Effects folder, and make a full screenshot.
It should show the contents of the folder and the full folder path in the address field.
Post the Direct Link, or thumbnail.
http://www.take-a-screenshot.org/
http://imageshack.us/