This error might appear if you have another function named "plot" on your path. Execute the following line to identify all functions named "plot" on your path.
>> which -all plot
If there is a user-defined function listed above the built-in, it may need to be renamed or removed from your path.
Note that you may see a number of other plot functions that are located in the MATLAB install directory. This is expected. They implement specific functionality for other built-in classes.
Apparently my 2010b version and my 2011a version were getting their wires crossed - so what Walter was saying was on the right track. Not sure how to best fix this - but I put a 2011a folder with all the files with the 2010b folder (the default install location apparently changed between these two versions), and for now it is working.
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