Hi Akintunde,
This problem generally means you have an inconsistent version of files in your installation. Could you have installed the R2013a SimBiology add-on in your R2012a Student Version? That could explain this problem. You may be able to confirm which the versions of MATLAB and SimBiology you have installed by running the command "ver" from the MATLAB command prompt.
SimBiology was first released as a general add-on to the Student Version of MATLAB starting in R2013a. Unless you received special instructions from your academic institution on how to install SimBiology for the R2012a Student Version, you will not be able to use SimBiology with the R2012a Student Version. If you did receive such instructions from your school, then I would recommend re-installing to make sure that you followed the instructions correctly.
-Arthur
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