请教各位，我用的是matlab7.2,在进行符号运算时总是报错，无法进行基本的符号运算，具体情况如下：

syms a b;
>> y=a+b
This error was detected while a MEX-file was running. If the MEX-file
is not an official MathWorks function, please examine its source code
for errors. Please consult the External Interfaces Guide for information
on debugging MEX-files.

If it is an official MathWorks function, please
follow these steps in reporting this problem to The MathWorks so
that we have the best chance of correcting it:

1. Send this crash report to segv@mathworks.com for automated analysis.
For your convenience, this information has been recorded in:
C:\DOCUME~1\new\LOCALS~1\Temp\matlab_crash_dump.2992

2. If the problem is reproducible, please submit a bug report via:
http://www.mathworks.com/support/contact_us/ts/help_request_1.html

Thank you for your assistance. Please save your workspace and restart
MATLAB before continuing your work.

Error in ==> maple at 113
[result,status] = maplemex(statement);

Error in ==> sym.maple at 85
[result,status] = maple(statement);

Error in ==> sym.plus at 22
X = maple(A(,'+',B();