When I was activating and customizing some extensions, this happened to me. The ACP page went blank and I was, understandably, worried that something had broken. What actually happened was I had my forum open in another tab and as part of the test process, I logged out and logged back in. I then went back to the ACP page to refresh, which is when it blanked.
On the newly logged in tab, ACP (and everything else) worked fine, so I am kind of assuming it has to do with the old session key being invalidated with my log out/log in. My suggestion is that instead of just having a blank page, add a notice explaining what is happening and why. That would alleviate a lot of confusion between a simple expired session key and an actual broken extension.