Hi,
Apologies; my colleague didn’t quite give the right advice. The free version does support Multisite; but without having the code necessary to differentiate between admins and super-admins. As long as all your admins are trusted, then that’s fine. (It also lacks some features that the paid version has, such as the ability to restore a single site instead of the whole install, or to import a single site into the multisite).
It’s a bit weird that de-activating causes a problem. When WP de-activates a problem, the result is that it stops running any of that plugin’s code. A problem that comes from *not* running code doesn’t make much sense! If you turn on WP_DEBUG in your wp-config.php, then instead of a blank screen, hopefully you instead get an error message. What is the error message?
David