XF 1.1 Private Messages - Couple old Odd Convertings

Hi everyone,

A while ago when I converted from IPB to vbulletin to Xenforo which run all good the PM's have shown up as unread which notes I have 216 unread messages. Is there a feature that I can tick that states "Mark all read" and some members are experiencing problems that they are unable to see PM's to each other. I have tried lurking into the Admin section but to me there's no clear cut options on that issue too.

Any help would be great!