$match_count += 1 if ($subject =~ /^[RE:\s*|FW:\s*]*$match_string\i*$/);

##</code><code>##

Nested quantifiers in regex; marked by <-- HERE in m/^[RE:\s*|FW:\s*]*Are you a Perfect Sinhalese??? 
<-- HERE ?\s*$/ at C:/Perl/lib/LTG/DocBuddy/Relation.pm line 496.