For such a small hack the install is pretty wacky.
Using 3.0.6 In profile.php I can't seem to find:
PHP Code:
$pm['forward'] = 0;
or
PHP Code:
$url = "private.php?$session[sessionurl]";
eval(print_standard_redirect('pm_messagesent'));
are you sure you didn't mean private.php instead of profile.php in the instructions?
I also don't see a "newpm" template. Are you sure you didn't mean pm_newpm?
That's all 3 edits, and all of them are fubar
edit: I went ahead and applied the changes in the read me to the private.php file and pm_newpm template instead, assuming that is what you meant, and it works fine

Thanks!