This was caused by the last update to the boards software. Here is the post from tech support that explains what was happening.
"They did an automatic patch this time for users on 2.3.6.. I don't particularly like it, but.. In a way it's good.. What's been happening, and you can see the Blog post through the link in your ACP.. Spammers have been manually registering accounts to get past the CAPTCHA.. Then using a script to automatically PM every user on forums.. Now, outside of the annoyance factor to you.. It puts a heavy strain on the servers, and because users usually are setup to receive an email when they get a PM.. Servers are being reported as sending spam via Email, and getting blacklisted. So, causing all kinds of problems. This PM flood control puts a stop to it.. But 5 minutes is a bit excessive.."
I have changed it to one minute. Anyone having issues, please contact me.
Lou