You did try to change the post content. The space sign is also a content data. Sending of that requires introducing of new additional date for the post. So the responsible addon , for instance the Change Content Owner or Date eg ... ( the alert is just of the addon ) needed to access the database and the system refused. For some reason , you was found you were not allowed to do it as a regular user. Just a minor crack IMHO.
A such error can happen because our forum system runs a couple of works to keep the forum clean and working properly. The soft is constantly changing/updating, etc. When you try to change something while the system is trying to do its work at the same time or one of its cron jobs is just in progress at the thread/post level you may get a such message suddenly. Just the system work is of the higher priority and an user has to wait until all is changed correctly. It should happen hardly ever or never. But it is possible and some of patience is needed. Usually in a couple of seconds the another attempt ends successfully. Certainly it doesn't mean you or your stuff got in trouble.