After fixing the code a bit (I would assume that to have been typos), the following code works just fine for me: 
use Tk;

$myForm = new MainWindow;

$angleEntry = $myForm->Entry(
    -width           => 12,
    -validate        => 'focusout',
    -validatecommand => \&angleCallback,
    -invalidcommand  => \&AngleError,
    -textvariable    => \$angle
)->pack;

$other = $myForm->Entry(-width => 12)->pack;

sub angleCallback
{
   my ($str, $newchar, $curstr, $index, $type) = @_;

   if (length($str) == 0 or $str !~ /^\d*.?\d*$/ or $str > 360)
   {
      $angleEntry->focus;
      $angleEntry->selection('range', 0, 'end');
      return 0;
   }
   return 1;
}

sub AngleError
{
   $myForm->messageBox(
      -title => 'Error',
      -message => 'Angle must be a number between 0.0 and 360.0',
      -type => 'OK'
   );
}

MainLoop;

[download]
Could you maybe provide a small script that reproduces your error?
CombatSquirrel.
Entropy is the tendency of everything going to hell.

In reply to Re: Problem with keyboard after entry validation by CombatSquirrel
in thread Problem with keyboard after entry validation by sfinster

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.