I am truly starting to believe that 4.5.1 has a serious flaw in it that is causing this problem when certain conditions are met.  There seem to be more and more people posting with the same symptoms as I'm seeing (this thread is just one example).  

The first hint I had was when I was originally upgrading from 4.5.0 to 4.5.1.  I would install the update, everything stopped working.  I restored 4.5.0, everything started working again.  I went back and forth like this about a dozen times, and it was consistent that the upgrade simply wasn't working.  I'd still be running 4.5.0 if I didn't accidently lose my backup, but that is a different story... *grumble*

The clincher was when I purchased a larger module a couple of weeks ago from a third-party vendor, and they had major warning about installing it on 4.5.1, complete with a diagnostic of what functions were not working right.  About that time I finally started thinking that it wasn't my install that was the problem.

I set aside some time today to get a second copy of DNN up and running today, I'll do some more testing.

I am so glad I'm not the only one experiencing this!  *grin*

I was hoping for an honorable mention in the 4.5.2 list!

Hey Alex, you come across anything on this issue in Gemini? If not I'll submit an issue. Danball, you say you have seen several versions of this issue, any of them reported in Gemini other than the AD provider?