With some TBS DVB-S/S2 cards scanning a MUX fails
With certain models of TBS Technologies DVB-S2 cards (the TBS 6905 is one example), if you go to DVB Inputs | Muxes and attempt to add a new mux, and set the Scan Status to PEND, it will try to scan the mux but always fail. However, if you go to the TV adapters screen, go to the associated tuner and click on the tuner input (the line that starts with "TurboSight TBS ...") and then TEMPORARILY change the values for the "Input Buffer (Bytes):" and "Skip Initial Bytes:" so that they are both zero (0), and then repeat the scan attempt, it works (assuming there is a valid signal on the mux you are trying to add, of course). After you have scanned the mux you can go back and change those values back to whatever they were before, and it will receive the scanned channels with no problem. This problem occurs even if "Skip Initial Bytes:" is already set to zero, until "Input Buffer (Bytes):" is also changed to zero.
I don't know why this happens and I realize this probably isn't enough data to suggest a solution, but if anyone else complains about not being able to scan a mux using a TBS tuner card you might have them try setting both of those values to zero. Note this is not a problem with some other TBS models (such as the older TBS 6985)
I'm still running TVHeadEnd 4.0.9 (waiting patiently for 4.2), so if this has already been found and fixed I apologize for mentioning it.