Undefined Function Errors in Matlab

I have used Matlab many times and I have installed a version 7.8 today after sometimes. Now when I am defining a character for symbolic expression, it is giving error. I also used google help for defining symbolic expression and also mathworks site. But still I get below errors. Am I missing something?

>> syms x y z a b c

??? Undefined function or method 'syms' for input arguments of type 'char'.

>> a = syms('a')

??? Undefined function or method 'syms' for input arguments of type 'char'.

>> sym a

??? Undefined function or method 'sym' for input arguments of type 'char'.