Why is a license needed? Or: your license is not GPL!
However, in your source file you state:
WARNING: This copy is made available to you under the terms of
the GNU General Public License and is not suitable for inclusion
into commercial or internal applications.
The license requirement for internal use is complete BS, since the only GPL requirement is to give away all code in the _intentionally distributed_ codebase. Since you still state this, you're trying to make the license not GPL and incompatible with other products! If you have a problem with people freely (as in speech, which can be commercial) using your free (as in beer) code, then GPL is not the license for you. You have to write your own.
Now to see how long until someone deletes this post...