Its the non-UTF character in your subject (’); if your forums were in UTF8 the character would process, but you're still using the iso-8859-1 character set which has been depreciated since the ISO "Working Group" disbanded in 2004.

An example of special characters in a subject line (its not an alphanumeric (A-Z0-9) issue (which would mean a problem with standard punctuation characters)) of a UTF forum can be found attached.
Attachments
smilesubject.png

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
Do you need Forum Install or Upgrade Services?
Forums: A Gardeners Forum
UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
Longtime Supporter & Resident Post-A-Holic
VNC Web Services: Code Modifications, Upgrades, Styling, Coding Services, Disaster Recovery, and more!