Can you make a working code example, that dosn't use any OO program? That would identify wheter it's a Wx problem, or an improper object model which you use.
You could also check the reference type of $self to see what you are getting.
sub Combobox1action {
my( $self, $event ) = @_;
print $self, "\n";
$self->SetTitle( 'Combo box selected' );
}
If $self prints out to be a WxWidget Combobox, your code should work. But if $self turns out to be the package you are holding your code in, MyFrame, a WxWidget frame, then you will need to find a way of clearly identifying the Combobox.