I created this routine to deal with this situation and do cut/paste/modify from javascript to code

sub doPostBack
{
    my $agent  = shift;    ## WWW::Mechanize agent-object passed in
    my $target = shift;    ## first argument in the __doPostBack() cal
+l in javascript
    my $arg    = shift;    ## second argument in the __doPostBack() ca
+ll in javascript

    # convert the passed in string
    $target =~ s/\$/:/g;

    $agent->form_number(1);
    $agent->field('__EVENTTARGET', $target);
    $agent->field('__EVENTARGUMENT', $arg);

    $agent->submit();

} #endsub doPostBack

# function __doPostBack(eventTarget, eventArgument) {
#    var theform;
#    if (window.navigator.appName.toLowerCase().indexOf("microsoft") >
+ -1) {
#    theform = document.MTMMAIN;
#    }
#    else {
#    theform = document.forms["MTMMAIN"];
#    }
#    theform.__EVENTTARGET.value = eventTarget.split("$").join(":");
#    theform.__EVENTARGUMENT.value = eventArgument;
#    theform.submit();
# }
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