Can't locate object method "new" via package "Win32::API" at foo.pl line 15.

So you're missing a use Win32::API;

I also have an unrelated issue with this “upgrade” because ActiveState has removed Perl/Tk from their ppm repository.

<Nelson Muntz>Ha-ha!</Nelson Muntz>

ppm install MinGW && cpan Tk

or ppm install http://www.sisyphusion.tk/ppm/Tk.ppd