I had a similar result happen to me a week or so ago.
I had just sent a PM, and then tried to send a minor correction almost immediately after the first one. I received the same message, telling me I cannot post another message so soon after the previous one.
I just assumed I did something wrong and re-posted my correction a couple of minutes later.
It's probably nothing or my phone, but I had sent a PM, then posted a reply to Mike's recent door panel work and the site logged me out when I submitted it. I don't have issues when I use the laptop, functions seem to be fine otherwise :2: