IP address issues and forum posting?

Hello guys.

Help please ..

I used to be able to post on a particular forum for months and it shows that I haven't been banned. I can log in and it says I have access to posting and viewing profiles, but when I try I get this message:

Error
Only members with sufficient permission can access this page.

This function is not available as you are using an IP address or range that is not permitted.
Please contact the forum administrator if you feel this is in error.

and

Error

You must be a registered forum member to view profiles.
Your Forum Membership is not yet activated!
To activate your forum membership click on the link in the activation email you should have received after registering.

I've tried both IE and fire fox, deleted cookies, temporary internet files, etc with no luck. Any suggestions on how to fix this?