Plugin activation and upgrading issues

I have searched for this answer, but I can’t seem to find the asnwer anywhere. I’m sure it’s there, but I can’t find it.

I’m running WordPress 1.5.2 I’ll get to upgrade in a minute. I’m running into a problem where I try to activate a plugin, and the plugin page tells me it’s activated, but in reality, it isn’t. It’s not just one plugin, but a few. Like Adhesive, or Canary Comments, or Tiger admin. I activate, and it says “Deactivate”, implying that it should have been activated… but nothing happens.

What should I do?

Also, I want to upgrade to WordPress 2.0. But my site currently serves around 8,000 unique visitors each day, and I’m worried that if I upgrade, the 2.0 version won’t work with the theme I’m using now, and I’ll get a bunch of readers looking at a broken site, while I downgrade. I’m using a slightly modified verion of Bionic Jive, from Theron Parlin. Anyone out there running it on 2.0?

Thanks