Unable to connect to Storage "•Cannot connect server to Storage"

I have reinstalled with RHEV 3 GA but am not having much luck adding Storage to my host via the GUI (using the IE browser). I can't find what the problem is, the export directory I have chosen either cannot be connected to:

"Operation Cancelled    •Cannot connect server to Storage""

or, if I use the directory I gave during the setup process of rhevm (rhev-setup), the error I get is:

"Create Operation failed. Domain OS-folder already exists in the system"

I was advised to delete the contents of the initial directory (as given in rhev-setup) but this has not helped. All new test directories I have tried simply cannot be connected to. I am using NFS, and I have checked NFS config in /etc/exports to ensure the directories are all there, with rw permissions, shared with all-comers IP-wise (*). Also I have 36:36'd everything so that user and group is "vdsm kvm".

Can anyone suggest anything that perhaps I have not tried?