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Hi,

This issue has been discussed many times. Sometimes solution offered by me helps to resolve it:

http://forums.autodesk.com/t5/forums/searchpage/tab/message?filter=labels%2Clocation&location=forum-...

If you need to save your plot styles before resetting (reinstalling) AutoCAD you can backup them now:
- at the command prompt type PLOTSTYLE, hit Return
- select "Reveal in Finder" from the drop-down list in the Plot Style window
- you will be redirected to the Finder window with the Folder where all your custom Plot Styles are.

Maxim