I've had a similar problem over the last few days. Even though the channel targets are showing that they are registered, IFTTT had been showing this error occasionally. Since last night, I've found that clicking on the Activate button won't even allow me to add certain sites. I've been getting no server response to the click. Several of my friends and colleagues have reported similar experiences.
All this leads me to believe that the servers on IFTTT's end may be overloaded. They released a long awaited client for Android just a few days ago, and that's when the problems seemed to start. IFTTT doesn't seem to offer any sort of forums or tech support that I've been able to find. Their Twitter channels @IFTTT and @TodayAtIFTTT don't show any commentary since the launch on April 24th either. At this point, I suspect we're going to have to wait and see. The main service seems to be working well for me thankfully.
It may be a matter of deploying additional virtual server instances to handle the increase in activation traffic. IFTTT runs on AWS (the Amazon Web Services platform), so that shouldn't be terrible difficult. While I know this isn't a definitive answer to your question, it's the best information I've been able to gather so far. Good luck, and I'll be sure to post more concise information as it becomes possible.