Vista Security is undoubtedly not allowing you to write the file in the root
directory of the C: drive.  Hard coding an output file location as you are
doing here was bound to fail sooner or later.  The answer is to create the
file in a place that the user has write privileges.  There has been lots of
discussion about this and other Vista related security changes.  You will
need to do a little reading on the subject.

As an aside you really ought to have an error handler in a routine like
this, where it wants to create a file.  I also do not understand why it is a
Function.  I do not see it either declaring a return type or returning a
value.

Ron W