Why can I only post once every 20 minutes? I have not posted a question in that last twenty minutes, I've only posted one answer. Does this rule apply to all users or just new users? At a minimum the count for questions and answers should be separated and the dialog box should be clear whether it applies to all user or (as I suspect) only new users. If it applies only to new users, this might be a reasonable rule for asking multiple questions, but penalizes new users for providing answers. Because I answered a question the system is now blocking me from getting an answer to my own question. Futhermore, I answered the question an hour ago. I only edited that answer in the last twenty minutes. Finally, and truly bizarrely, while the answer was on ask ubuntu meta, it still will not let me post a question on ask ubuntu, but it allowed this question here.
It looks like you are using the same IP as a bunch of other people. At least one of them is suggesting edits that have been marked as spam. These are anonymous suggested edits, so it's not you or any other user on this site; just someone who shares your IP.
Unfortunately, we don't have an easy way to tell the difference between legitimate users and spam users from a particular IP except by reputation. Our automated checks occasionally catch new users who happen to be coming from the same IP as malicious users. So the only thing I can suggest is to wait it out or use another IP to log in.
According to The Complete Rate-Limiting Guide on the main meta site, users with less than 125 reputation may only post a question every 20 minutes, and may only post an answer every 3 minutes. As far as I know, these limits are per site. In this case, the message should tell you which limits apply.
When you have low reputation (I think 40 is still low), if someone has been sending spam from your IP address, or if someone with a history of low-quality posts has been using your IP address for a while, you may be more restricted than normal. These limits are not documented precisely (to avoid spammers who post spam every X minutes by the clock).
I'm sorry, it does suck if you get caught in the backlash against a spammer, but the current spam filters have been very effective in eliminating a lot of manual cleanup work, so we can't do without them.
I do think that the filters shouldn't apply to you — you have a network account in good standing, and you'd have more than 100 rep here if you hadn't offered a bounty. The filters should probably not count bounties, or take the maximum reputation accross the network into account. Maybe it's too expensive to calculate a better number than the site reputation, however.