It can be difficult when using terms like
table in XPath as this is so dependant on the overall document structure. It's better if you can pick up on something like
<b>Contracts</b> as part of the table your interested in and search for that table.
So you could try...
print $xpath->evaluate('sum(//table[td/u/b/.="Contracts"]/tr[position() > 1]/td)');
To help work out what it's doing you can break it down to levels and see what it's returning. To check if it's finding the table, use...
$table = $xpath->query('//table[td/u/b="Contracts"]'); echo $doc->saveHTML($table);
Then add onto it to see where it's failing. One of the big difficulties can be that as your using HTML, is a constant problem of bad HTML gets converted into XML and it can loose some of it's structure.