can't upgrade or install 2.7

[cess]

Hello,
I'm trying to upgrade to vshare 2.7 and after the upgrade I keep getting "user not found" errors. It happens when I click upload, login, register and a lot of other links. Some of the pages won't even show, it's just the main page with "user not found" on it after clicking links on the site. I tried a fresh install but still get same error. Any idea how to fix this?

TIA

[buyscripts]

Reupload .htaccess

Also check in error log