Backup location access denied SQL 2008 R2 Cluster

Hello,

I have a SQL 2008 R2 Cluster, 2 nodes (Windows 2008 R2 Enterprise SP1).

I can add the path manually, but I cannot select a backup destination , I get this error:

Then , empty directory, cannot see the clustered disks:

I checked the dependencies, both disks (DB & Logs) are there. I granted SQL service account full access on both disks. I use (run as administrator) when running SQL management studio.

Any ideas?

Thanks, Shehatovich