Sounds like you're doing something weird in there; you should probably check your error logs or do the full use CGI::Carp qw(fatalsToBrowser warningsToBrowser);. All those examples should work fine.

Another thing you might consider is the Vars() idiom is a little strange today. There is no reason to avoid the param() function in favor of it. Your code above becomes (with a little HTML formatting help):

print '<ul>';
for my $sri_variable( param() ) {
    print '<li>', $sri_variable;
    print '<ul>';
    for my $variable_value( param($sri_variable) ){
        print li($variable_value);
    }
    print '</ul></li>';
}
print '</ul>';
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Make sure to use strict; use warnings; too. It looks like you're not. (update: fixed bad HTML nesting.)