The following code produces some odd behaviour with respect to sybase connections.

 for ($i=0,$i<10,$i++) {
1.   $link = sybase_connect("x","x","x");
2.   echo "Link ID = $link -- ";
3.   sybase_select_db("x");
4.   $result = sybase_query("select ...");
5.   echo "Result ID = $result";
6.   $row = sybase_fetch_row($row);
7.   echo "query result = $row[0]";
8.   echo "------------- <br>";
 }

This code gives me the following output:
Link ID = Resource id#1 -- Result ID = Resource id#2 
query result = x
------------- 
Link ID = Resource id#1 --
Warning 1 is not a valid Sybase-Link resource in line 3
Warning 1 is not a valid Sybase-Link resource in line 4
Result ID =
Warning Supplied argument is not a valid Sybase result resource in line 6
query result = 
--------------
The above pattern repeats itself with the Link ID now Resource id#3 and Result ID = Resource id#4, etc

Removing Lines 6 and 7 gives :
Link ID = Resource id#1 -- Result ID = Resource id#2 
Link ID = Resource id#1 -- Result ID = Resource id#3 
Link ID = Resource id#4 -- Result ID = Resource id#5 
Link ID = Resource id#4 -- Result ID = Resource id#6 
Link ID = Resource id#7 -- Result ID = Resource id#8 
Link ID = Resource id#7 -- Result ID = Resource id#9
etc

Adding a sybase_close fixes the problems
Link ID = Resource id#1 -- Result ID = Resource id#2 
Link ID = Resource id#3 -- Result ID = Resource id#4 
Link ID = Resource id#5 -- Result ID = Resource id#6

PHP modules: --with-apache (1.3.12)
             --with-sybase-ct (11.0.0.3)
             --enable-trans-sid

PHP.ini : default except for sybase severity errors on 11

Hope this helps
Thanks
David Clark