Drive

With Google Apps, domain administrators can restrict users from receiving documents sent from outside of their domain. If this option has been enabled, you'll receive the following message if you're outside the domain of the person you'd like to share with:

We're sorry, this document cannot be shared with (email address).

In order to share with this domain, the administrator will need to enable the following option:

Let users receive documents from outside this domain.

For assistance, we recommend having your collaborators contact their domain administrator directly.