Hi Florinel,
We had simular issues with an environment running 8.1.1, Citrix and Windows 2008 R2/Windows 7 systems.
After opening cases for this with NetApp, Citrix and Microsoft, they told us this has to do with the way CIFS/SMB is operating on the NetApp systems.
Connections to files were blocked, or not responding anymore.
Because we had folder redirections, sometimes systems were not responding anymore and gave us huge problems.
After upgrading tot 8.1.2. the problems dissapeared.
I have seen a lot of customers with file blockings, slow connections and not responding clients on 8.1.1. and SMB enabled.
There are some solutions, disabling SMB v2 is one, and not to use folder redirections.
But the only thing what I have seen working, is upgrading to 8.1.2.
Then also folder redirections and SMB v2.x will work.
I hope this will help you,
Arco