Verify that you have the menubar open. Type MENUBAR at the command line, and reset it to 1. Also, if the software is loaded, and PLANT just doesn't show up on the menubar, type LOADLANGPLANT at the command line, this will reload CADWorx inside AutoCAD and typically will reload the dropdown as well. Lastly, if the software just isn't loading up in AutoCAD, create a new profile by going to Programs>CADWorx 2010>Plant> Create Profile-Plant. This will put a new icon on the desktop, use that icon to initialize the software.
CW 2011 is not available, but the latest build of CW 2010 is ACAD 2011 compatible.
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Kyle Pope