mex Error: Could not find the compiler "cl" on the DOS path?!!

please I need your help! I have downloaded a program written in C, and wish to run it in Matlab. To do this is use the mex to compile it into Matlab. This has worked for me with R20013a. However, I tried to use it today with R2008b and I got the error;

 >> mex FiltreShenCastan.c
Error: Could not find the compiler "cl" on the DOS path. 
Use mex -setup to configure your environment properly. 
C:\PROGRA~1\MATLAB\R2008B\BIN\MEX.PL: Error: Unable to locate compiler. 
??? Error using ==> mex at 213
Unable to complete successfully.
>>

and then when I do mex -setup

    % >> mex -setup
      Please choose your compiler for building external interface (MEX)     files: 

     Would you like mex to locate installed compilers [y]/n? 

    Select a compiler: 
    [1] Microsoft Visual C++ 2008 Express in C:\Program Files     (   (x86)\Microsoft Visual Studio 9.0 

       [0] None 

       Compiler: 1

       Please verify your choices: 

       Compiler: Microsoft Visual C++ 2008 Express  
       Location: C:\Program Files (x86)\Microsoft Visual Studio 9.0 

       Are these correct [y]/n? y

     ***************************************************************************** 
       Error: Could not find the 64-bit compiler.  This may indicate that   the  
        "X64 Compilers and Tools" or the Microsoft Windows Software  
         Development Kit (SDK) is not installed.  To build 64-bit MEX-   files  
          Microsoft Visual C++ 2008 Express Edition requires that these  two  
          packages are installed properly.  
 ************************************************************************* ****

Trying to update options file: C:\Users\mariem\AppData\Roaming\MathWorks\MATLAB\R2008b\mexopts.bat From template: C:\PROGRA~1\MATLAB\R2008b\bin\win64\mexopts\msvc90freeopts.bat

Done . . .

************************************************************************ Warning: The MATLAB C and Fortran API has changed to support MATLAB variables with more than 2^32-1 elements. In the near future you will be required to update your code to utilize the new API. You can find more information about this at: http://www.mathworks.com/support/solutions/data/1-5C27B9.html? solution=1-5C27B9 Building with the -largeArrayDims option enables the new API. ***********************************************************************