Well, spoke to soon.
Now that I can access the pm feature, I actually can't send one out.
Instead I get the following message:
Oops! We ran into some problems.
Your content can not be submitted. This is likely because your content is spam-like or contains inappropriate elements. Please change your content or try again later. If you still have problems, please contact an administrator.
I have edited my message down to a one liner and still - no change.