Telligent 10 /administration not loading

We're upgrading from 8.x to 10.x. When we point the filestorage connectionString to our existing 8.x filestorage directory, we get a blank /administration page, even though the front-end loads fine. There don't seem to be any relevant errors in the cs_exceptions table. 

Note that our existing filestorage in on another server:

<add name="FileStorage" connectionString="\\servername\filestorage"/>

When we set the filestorage back to the default 10.x ~/filestorage/ directory, the administration section starts loading.

Any ideas what the problem is?