There are several situations where a policy rule will just generate an error to the user.
- block file transfer will gave user an 'error in transfer';
- external meeting invite to federated Partners without federation permissions, will just generated 'error establishing conference.
This cause a lot of confusion and stress to users and they need to call to support just to say "it's normal"
If we look at the lync log the error we find the reason for the error. Why Lync Client will not just display to the user that: "file transfer disabled by policy"