We've dealt with this problem in 2 ways.
Does your enterprise allow connections from outside your ip network?
Depending on your SSO setup it might affect how much of domain the security is looking for. For us it could either use no domain, or , @ufl.edu, or @AD.ufl.edu
I actually have another problem now.....
I added my students using the following method:
They are not able to use their college login credentials to get in. ArcGIS added _AllanHancock to their login names, but that doesn't work either (I hope that makes sense).
Thanks!
It turns out the organization URL did not match the college website URL....thanks for the quick response.