I received an e-mail today from one of our members, he said -

I received this error message when trying to post today:

The host from which you are accessing the board is not recognized as a valid host. This is more than likely related to a firewall issue that is blocking the referer variable. Check your firewall settings and try again.

Any ideas? Nothing is different with my system than previously.

Do you have an answer that I might give him about this? Thanks in advance.

I've had similar problems in the past and it was the HTTP Referer Check. I disabled it and haven't had any problems since.

CP > Primary Settings > General tab > Advanced Options > Disable HTTP Referer Check?

Earlier thread related to this here: "valid host" / firewall error?

rWe have many threads here on the topic; as SK points out, it's a security feature in the forum software. You should find information on it by searching these forums for "referrer check"