I have a WPMu installation on a closed network, and one blog is using the K2 theme, but the Text Widget is not offered as an option. When I switch the theme to Default, the Text Widget is offered. If I use K2 on another blog in the installation, I can see the Text widget. Any ideas on why the Text Widget won't work on K2 on this specific blog?
A reason for this can be that the Widget configuration data (that is what is stored into the database) is mixed-up on that certain blog. Those cases are hard to debug. What you can try is to reset all widget settings on that blog. Sometimes it's enough to remove the Text-Widget from the lower pane if it is available there. If not, remove the widget configuration from the database (backup first!). After that, the Text-Widget should be offered again.