There are three PHP 7 incompatibilities in the redirection script:

1) Line 55

Replace:
PHP Code
set_magic_quotes_runtime(0);
With:
PHP Code
//set_magic_quotes_runtime(0);

2) Line 91

Replace:
PHP Code
$query_string = split('[;&]', trim($qs));
With:
PHP Code
$query_string = preg_split('/[;&]/i', trim($qs));

3) Line 109

Replace:
PHP Code
$pathinfo = split('\/', trim($pi));
With:
PHP Code
$pathinfo = explode('/', trim($pi));

This should fix the 500 error