carver, your issue is actually different from that of the OP.
Your screen name has a space in it. The software will open a window pre-addressed to the recipient's screen mane, except when the name has a space in it. In those cases you must type in the name of the recipient. This is because the software "parses" the screen name and stops at the space...
In the case of the OP, only those who have contributed to the forum can send/receive PMs. This was implemented as a security measure when it was abused by a non-contributing member.
There. That should cover all bases...