[Plugin: WP Contact Form] Plugin could not be activated because it triggered a fatal error.

And you have the latest version of that plugin?

Yeap, absolutely.

I am having this same issue. I just upgraded from 2.3.1 to 2.5 and am getting the fatal error. I have installed WP-ContactForm 1.5.1.
It does not say what the error is.

me too me too

Could be conflicting with another plugin, try disabling all your plugins and just activating the contact form to see if that works. Then one by one reactivate the others until you work out witch plugin is causing a conflict.