Well, you've got two open-curly-braces, but only one closing brace. PHP issues an error after the last line because the end of the file had been reached and the matching closing curly-brace was never found.
Open curly braces are on lines 26 and 30. Your only closing curly brace is on line 37.
Errors like this are almost always detected if you're more consistent with your indentation and formatting. Here's your code, reformatted:
<?php
if($query_data)
{
echo "<tr><td width=\"";
echo "100%\" align=\"center\"><select name=\"selectuser\"><option value=\" \"> </option>";
while($query_data=mysql_fetch_array($result))
{
echo "<option value = \"";
echo $query_data["username"];
echo "\">";
echo $query_data["username"];
echo "</option>";
}
echo "</select></td></tr>";
?>
If this were properly nested, there'd be a closing curly-brace at column 0 (i.e. no indentation). After looking at the code, I think you need a closing curly-brace after your echo "</select>" line (line 39).
Take care,
Nik
http://www.bigaction.org/