Forced to log-on twice?

Hi all, long time lurker first time poster,
Recently I've been experiencing a weird issue with my notebook, and i'm not too sure what the first point of call should be to troubleshoot. Every time I log into my machine (high-end 2010 MacBook Air '11), it will without fail get me to log on twice. Basically it works as follows:
1) Boot up machine and it takes me to login screen (there is only one user accout on the PC)
2) Put in credentials - here it processes something for a while before my machine reboots
3) Takes me back to login screen without any acknowledgement of what happened
4) Login again and it takes me into my profile fine (at the normal fast speed you'd expect from the MBA)

I'm currently on 10.7.2 but I've been experiencing this also on 10.7.1.

My apologies if I've posted this in the wrong forum
Thanks

 

That's an extract of the ERROR from the console log. It's much longer.

How would I troubleshoot the disk permissions?

 

That option is greyed out and on "off". Tried to create another user to see if it was because there was only one user but didn't help.

edit: according to https://discussions.apple.com/message/2326872?messageID=2326872&#2326872 - That can't be enabled with FileVault turned on (which i have)

 

bump.