That session timed out issue is pretty common. First I'd recommend clearing your browser's history and cache (that way it'll delete any cached pages and anything else that may be interfering with your log in) and log out of the forum completely. Once you've logged out, relog using the box under the banner, not the yellow box on the side of the banner. If that shows no improvement, use another browser such as Firefox or Google Chrome.
As for sending messages to other users, that's a forum glitch--the forum is not always good when it comes to sending messages to someone who unfortunately has the same nickname and/or username. An easy fix to this is simply typing in their username instead of their forum nickname, since there's no same usernames, in the "To:" input, or maybe even adding that user to your forum buddy list, and then searching them through the "find members" tab. You can also type their forum nickname in the "find members" tab and look at the results that pop up, however if their username is not known, and they have a common forum nickname, it will be very difficult to sort through the results and successfully PM them.
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