When I upgraded to PHP 5.1.2 (from 5.0.x) I got the same problem as you: JCross and JMatch would't work and the Overview report didn't show.
The reason was that apparently in PHP 5.1.2 you are not allowed to assign variables in calls to functions, so some of the HotPot code was not working. (a more detailed explanation is at the end of this message)
I have modified the relevant HotPot code now and tested it on my PHP 5.1.2 server and everything seems to be OK again. You can download the new module form the Moodle downloads page tomorrow. The new version number is HotPot v2.1.15 (or 2005090715)
many thanks!
Gordon
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assigning variables when calling a function
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Consider the following PHP function, which is intended to add one to a number:
function add_one(&$number) {
$number = $number + 1;
}
Now let's say the function is used as follows:
add_one ($n=1);
print $n;
print $n;
In PHP 5.0 (and less) the print statment would print "2", but in PHP 5.1 the $n is unaffected by the function call and stays at 1. The solution is to assign the variable before the call to the function, as follows:
$n = 1;
add_one ($n);
print $n;
add_one ($n);
print $n;