If you were accessing the variable as $varname instead of $GET['varname'], then yes, there could have been a configuration change; namely, "register_globals" was probably turned off. The simplest fix would be to add a line at the top of the script to set the variable in question equal to its $GET array element:
<?php
$varname = $_GET['varname'];
However, note that this may not fix everything should there be cases where the variable was referenced within a function. In those cases, you will need to declare $varname as global within that function:
function myFunc()
{
global $varname;
// rest of function
}
Alternatively, a better solution might be to do a global search/replace on $varname, changing it to $_GET['varname'].
(Of course, another solution would be to get register_globals turned back on, but all recent versions of PHP have it turned off by default for a reason.)
