First of all, please learn how to attach a log to a message on a board... Simply zip it and attach the zip file to your message:
do not post the log in plain text ! I snipped the log and removed the spammy messages... More work for me, more work for you: bad solution !
Only attach the log corresponding to a failed session, where you will have opened the problematic profile, so that I can spot what warnings the viewer issued at that specific moment.
Then, obviously, that's something fishy in your only failing account, don't you think so ?
In any case, I spotted the following issues in the log you posted:
Obviously, the viewer cannot even open your account settings files, meaning there is a permission issue, or a missing directory, or a corrupted/failing hard drive issue on your system for that particular Windows user account.
Also, the proxy is badly configured, which could cause failures for the viewer to reach some SL servers...
I cannot investigate more accurately just from logs, but it's definitely something wrong on your computer(s), not in SL, not in the viewer...