Problem installing PowerPress

I’m trying to install PowerPress plugin but after I activate the plugin — I mean press the activate link — I get an empty page — no message so clearly something is wrong. The site is using WP MU but I didn’t install it so I am not sure how to find out what WPMU version it uses. Are there some compatibility problems that I should be aware of? According to the PowerPress documentation it works fine with WP MU.