It is more an idea than an problem.
If you are viewing someone's profile, and get the sudden need to say something to him, maybe you can add a button to it so you can send him a private message. So you don't need to write his username down and type it again when composing a private message
When you're viewing a member's profile, there is an "Private Message" section with the "PM" marked icon. When you click on the icon, it will take you to the private message area so you can type the message.
Despite the error you might be receiving, I can confirm that the message is getting to the intended recipient.
From what I've seen, the error usually will pop up when the recipient has requested to be notified via email when a new PM arrives. The system tries to send out an email, but never succeeds, hence the error.
We'll look into it once a few more important issues are resolved.