In the future please use the search feature before posting as this issue has been covered in a various ammount of threads.
The issue at hand is generally one of two things.
1. The URL you're posting from isn't on the list of valid hosts in your control panel (CP -> Master Settings -> Primary Settings -> Advanced Options -> Domains for HTTP Referrer Check).
2. You have a virus scanner or firewall that blocks the referralurl in your browser; this is common of Symantec and Norton products.
If #1 is the culprit then you'll need to add in any additional domains (also, be sure you have both a WWW and NON-WWW url listed for each domain possible of being posted from:
https://www.ubbcentral.com/|http://ubbcentral.com/
If #2 is the culprit you'll need to either disable the security setting in your control panel (which is NOT recommended as you'll be nerfing the security of the posting system to validate posts are coming from where they're supposed to be coming from) or you'll need to disable the masking of the referrer value in your firewall or virus scanner.
