Question on 6.0005

I am using Dolphin 6.0005 and have had a few comments from members where they have sent messages to other members, if they put say "Hi" in the subject line of the message, then the message will not send. They have to put more than 2 characters in the subject line. Is there a setting for this in admin? I have searched the forums here and in Expertzzz also looked throught admin panel but not found a solution so far. any help would be greatly appreciated.