An internal error has occurred.

Acrobat plug-in.

Could not find Acrobat External Window Handler Plugin.

Could not launch Acrobat.

http://www.adobe.com/acrobat/userinfo/exchange/3.0/

http://www.adobe.com/acrobat/userinfo/reader/3.0/

This operation cannot be completed until you close a modal dialog (e.g. the Open File dialog) in Acrobat.

ITA