Can you check the generated code of your instantiation screen. I guess in your getTSuser.ipl you should return output an xml starting with < select... > < option..... /> < /select >Wheras, you are sending the complete xml file.
try removing the ?xml from the beginning of the substitution.
Even that didnt help.:-(
$option= $option.qq(<option label="$pattern" value="$pattern"/>);
$option .= qq(<option label="$pattern" value="$pattern"/>\n);