Tk and Tkx are different, and the callbacks need to be set up differently. I don't have Tkx running on my Linux box, but from looking at the Tkx documentation for callbacks to Perl it shows this syntax for a validate command. 
  $entry->configure(-validatecommand => [
        \&check, Tkx::Ev('%P'), $entry,
    ]);

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In reply to Re: Tk vs Tkx for -validatecommand by zentara
in thread Tk vs Tkx for -validatecommand by shortyfw06

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