Give this a try (the id field on the multiselect should match the #<heading> in html)
<form onUnloadCancelJobs="true" >
<label>...
<description>...
<fieldset autoRun="true" submitButton="true">
<html>
<style type="text/css">
#input_unit {
width: 440px;
}
</style>
</html>
<input type="multiselect" token="yourtoken" searchWhenChanged="false" id="input_unit">
<choice value="*">All</choice>
......
......
</input>
</fieldset>
...
