in reply to Tk::JBrowseEntry gives me this error I dont understand

The problem appears to be that the only assignment to $w->{-borderwidth} is the return value of delete $args->{-borderwidth} at line 255, and then only if $args->{-borderwidth} is defined. This leaves $w->{-borderwidth} with the undefined value. I can't get to a machine with Windows to test this, so I could be missing something.

If I'm right, the quickest solution would probably be to specify a value for the -borderwidth attribute in your constructor. A -borderwidth value of 0 (zero) might be a good starting point (this is effectively what you're using now). If -borderwidth => 0 doesn't look right, experiment a bit.