General help

I'm having trouble importing a lesson. I go through the steps leaving only the one lesson I want to import checked. It starts the process but when it gets to about 92% it locks up and all I get is the wheel of death in my tab. I've had this happen on a few others and even though it didn't finish it finally showed up in my course but the pages were all mixed up. I've had other lessons import with no trouble of all.  The only difference I see is that the ones that give trouble are the ones that have clusters. I've had the same difficulty with restoring a course. It would restore the course up to the point where it would start loading a lesson that would have a cluster.