MATLAB: Will upgrading Matlab or Excel fix this problem

guiMATLAB

I have some code which reads .xlsx (Microsoft Excel) files. It works on a PC with Matlab R2012a. I don't know what version of Excel that machine has.
I brought the code to my machine. I am using Matlab R2009a and MS Excel 2002 (which might even be corrupt). When I run the code on my machine, I was getting an xlsread error which said the .xlsx file was not MS Excel format (I no longer have the exact error message).
I thought the problem might be my outdated Excel application, so I installed the Excel viewer. But now when I run the code I get repeated errors "Undefined function or method 'isappdaclearta' for input arguments of type 'double'" from "gui_mainfcn" (part of Matlab). I tried uninstalling the viewer, and I still get that error.
I cannot find any function named 'isappdaclearta' and a web search of that name did not produce anything either.
Questions: 1) Does the version of Excel matter to the xlsread() or gui_mainfcn() routines? 2) Will upgrading my Matlab likely fix these errors? 3) What could be wrong? (And how do I fix it?)
Answer was a combination of the two answers below. I needed a new Excel version (or possibly the Excel viewer) and I corrupted the Matlab toolbox file gui_mainfcn.m. Not sure who to credit.

Best Answer

XLSREAD calls the Excel COM api to open the file. If the 2002 version of Excel does not support *.xlsx, which a quick search indicates it does not, then you'll need a newer version of Excel. Alternatively, you could export the *.xlsx file as a *.csv and then read it in with csvread.