The moderators and I have banned literally thousands of spammers from the Hypnos Forum over the years. We ban them by username, email address and IP address. It's likely that when you're traveling (especially in Asia, as many spam accounts come from IP addresses in Asia) you're using an IP address banned by the forum. And probably the reason it sometimes works when you quit and try again is that you obtain a new, slightly different IP address that is not on the ban list.
It's nothing you're doing wrong. It's the unfortunate side-effect of spammers having flooded forums like these, trying to post advertisements and Search Engine Optimization links, that we've had to spend a lot of time and effort taking action against them. I apologize for the inconvenience, but especially when traveling in certain countries (China, Hong Kong, Malaysia, Indonesia, Russia, India) public networks are more likely to give you an IP address in a banned range.
The only solutions I can think of solving this when it happens would be:
1. disconnect WIFI and re-enable it, and hope you end up being assigned a safe IP address
2. if you're going to be at the IP address for a while, email me the date and time of the error message you're receiving and I'll look in the forum error logs to see which ban setting is keeping you out, then I'll remove that IP address ban
Sorry about the trouble!