[vdr] cFemonOsd::Show() cannot open frontend device

When trialing vdr-femon-1.1.0 with vdr-xineliboutput-1.0.0_rc1 I receive the following error when trying to view the signal information of my recording server via my streaming only client.

ERROR: cFemonOsd::Show() cannot open frontend device.

Is this a known problem or is there something more I need to configure for my specific setup?

[I need Femon to investigate dvb-t signal issues:- with vdr running the signal to my old freeview settop box is degraded to an unusable level. Signal from common aerial is being split with a "1 in 2 out" signal amplifier. There's a 25m cable to the vdr server and a 12m cable to the set top box.]

Any advice gladly received!