Hi there,
I had the same problem recently after re-installing vCenter. I could log in fine to VDP but I got the same storage error and when I tried to register VDP it kept failing authentication.
What I found is that although I had added the account I use to authenticate VDP in the web client I had to also add this account to the thick client.
log in to vSphere vClient as root.
With vCenter as the selected object navigate to the Permissions tab.
right click and select Add Permissions...
Add the account that you use to authenticate VDP as an Administrator.
This fixed both the storage issue and the registering issue.
I hope this helps, if not try this; VMware KB: vCenter Server Appliance 5.5 root account locked out after password expiration
Your Root account may be locked and if you are using that for authentication it will break.