[2.1b1] Can't use custom image repository

ct 5 13:12:37 unleashed maas.import-images: [INFO] Downloading image descriptions from /var/www/html/images/streams/v1/
Oct 5 13:12:37 unleashed maas.import-images: [WARNING] I/O error while syncing boot images. If this problem persists, verify network connectivity and disk usage.

==> /var/log/maas/regiond.log <==
2016-10-05 13:12:37 [-] Error on request (51) bootresource.fetch: Mirror provides no Ubuntu images.
        Traceback (most recent call last):
          File "/usr/lib/python3.5/threading.py", line 862, in run
            self._target(*self._args, **self._kwargs)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 801, in worker
            return target()
          File "/usr/lib/python3/dist-packages/twisted/_threads/_threadworker.py", line 46, in work
            task()
          File "/usr/lib/python3/dist-packages/twisted/_threads/_team.py", line 190, in doWork
            task()
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
            result = inContext.theWork()
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 834, in callInContext
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 603, in call_within_transaction
            return func_outside_txn(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 422, in retrier
            return func(*args, **kwargs)
          File "/usr/lib/python3.5/contextlib.py", line 30, in inner
            return func(*args, **kwds)
          File "/usr/lib/python3/dist-packages/maasserver/websockets/handlers/bootresource.py", line 701, in fetch
            raise HandlerError(err_msg)
        maasserver.websockets.base.HandlerError: Mirror provides no Ubuntu images.