Odd error after upgrading from Php4 to Php5

["Ian Barnes" <barnracoon@xxxxxxxxx>]

Hi,

We recently upgraded our primary webserver to php 5 from php4 and we are now
getting the following errors on the site:

*Catchable fatal error*: Object of class stdClass could not be converted to
string in /home/www/somesite/somfile.php on line *199

*Around that area in the code is some code something like:

if(!$db->query("SQL QUERY HERE"))
{
  echo 'Fail';
}

Any ideas what it means or how I can fix it ?

Thanks
Ian

P.S. Please copy me, i dont know if my list membership is working.