Flex SDK 3 Compiler problem with php

Dear All,
Thanks in advance.

I have the following problem
When i execute following line from my command prompt
c:\flexsdk3\bin\mxmlc.exe c:\users\222131\Simple01\Simple01_222131.as -output c:\out.swf

It works fine.,

But when I do the same with
exec(“c:\flexsdk3\bin\mxmlc.exe c:\users\222131\Simple01\Simple01_222131.as -output c:\out.swf”) in php it doesnt work.

Can any one help with this.?

Thanks