Don’t know if this will help but here is my story.
I upgraded to 2.7 and had just about every problem you see here and a few more, my blog was all but dead.
I tried everything I read and still it was not working. I had decided to scrap it and reinstall the older version.
In the admin area under tool I saw a reinstall button, I thought what have I got to lose.
About a minute later it said install complete.
100% of all the troubles repaired.
Give it a try, worked for me.
