what is a "valid link resource"?

In trying to learn both php and postgresql as a novice, I am trying to
debug a double migration of our old website from php4 to php5 and from
postgres 7.4 to 8.3.
I am running freebsd 7.0 on two machines and sometimes debugging from a
Windows XP.
The migrations themselves went fine; now to debug and make them actually
work so I can tear this thing apart and rebuild with a new concept,
design & implementation.
So far, I am getting this error:

"pg_exec(): supplied argument is not a valid PostgreSQL link resource"
in this code (third line -->)

...snip
function SQLQuery( $query ) {
    global $dbh,$curr_row,$result_hash;
    if( !($r=pg_exec($dbh, $query)) ) {
    if (error_reporting()>0) {
                echo "<hr>SQL error (".pg_ErrorMessage($dbh).")<br>in
($query) <hr>";
    }
        return 'error';
    }
    $curr_row[$r] = 0;
    $rows=@@pg_numrows( $r );
    if(eregi("insert",$query)) {
    #list($f1,$f2)=split('INTO',strtoupper($query));
    $f=array();
    if(eregi('(.*)into(.*)',$query,$f)) {
        list($tablename,$bullshit)=split("\(",$f[2]);
        $result_hash[$r]=$tablename;
    }
    }
    return $r;
}
snip ...

What, then, is a valid link resource? is it the strings or their
content? I have been trying to figure out if pg_exec is valid in
postrgres or should it be replaced by another function? There seem to be
a number of these functions that are returning the same error...
I have also not been able to determine the content of  the strings $dbh,
$query or most other strings while debugging with eclipse, trying with
phped, devphp .... I seem to be connecting to the remote server (freebsd
with apache2.2.8 on LAN)

Thanks for any help or suggestions...