I got issues with Groups not visible in any Viewer, Tp not working at all, Sims near by not accessible, not visible.
The root cause for it was the "Ready Boost" USB stick i created and didn't have Active/available when logging in to secondlife.
My solution for the issue: System restore to when "Ready Boost" was not enabled. If you have your "Ready Boost" media avaliable, remeber to have it enabled.