It's either permissions or the path changed. If you can connect to this path still from your system, then you have a permissions issue. Perhaps a password changed? It might be that the password was the same for both sides in a workgroup-type setting for the adminstrator account (or other account). If you have a domain account for SQL Server (service), then check permissions.

Typically the admin shares aren't used for this because they can require some permissions you don't want to give, or need. Create a normal share and assign permissions.