UBB.threads PHP Forum Software Community Forums UBB.threads 6 Version 6 Support Blacklisted? Incorrect message being received

I'm still using v6.5.5 and will be upgrading to the latest v7 asap.

But currently some of my members are receiving a "blacklisted" message when trying to log in to the forums. If they re-try say several times they eventually get through.

These members are not banned.

I have removed all the IP addresses that were on the banned lists.

It is still occurring.

Furthermore I thought UBB uses the word "Banned" not "Blacklisted"?

What is going on? Has my ISP account of forums been hacked?

Thanks.