I often send out friends requests because I need to contact someone privately. So why is it when I try to send a message, I'm getting this message a significant number of times?
You are not authorized to send messages to this member
It can be chalked up to oversight on the part of a new person I suppose accidentlally unchecking the box that allows messages to be sent. That box is there for a reason to allow you to block messages from contacts that are harassing you with unwanted junk.
If you are not being harassed that block chould be checked allowing people on your friends list to contact you. APSense moderators try to use the messaging system to contact you privately when we see an issue arise rather than publicly. But if we cannot send you a message, we cannot do that.
Please check your friends settings and ensure that they allow messages especially from the moderators.