We had added it to trusted sites, yes. As I say, it has been working fine for a long time (years, in the case of some servers) and now just suddenly stopped. I loaded Chrome on one of the servers and it actually works.  I guess it is an IE issue.   Still very strange that it works in IE on a few servers but not on most of the others. 
We have about 15 PowerEdge servers and all but 2 or 3 get errors when trying to use OM Server Administrator.  A couple months ago, they all worked fine.  Not sure if Windows Updates caused it or what. They get the error "This page can't be displayed" when opening server administrator. I can find no rhyme or reason as to why this is happening.  It happens on R710s, R720s, and an R730, and also on some older R515s.  I have tried different versions of Openmanage, updated to 8.3 and it didn't help.   It also occurs on servers running both Windows Server 2008 R2 and 2012 R2. One R720 of ours is identical to another and one works, the other doesn't.  They are identical hardware (purchased at the same time), same OS, same firmware, same function as Hyper-V servers.  Why does one work and the other gets the error?  No idea. Any clues?   Thank you. 
Open Manage Server Administrator not functioning on almost all servers