This is what I've found so far. R5D1 +.20 would transcode sometimes if a cut point didn't run off either end of the recording.
I upgraded to R5E50 and then the cut points could run off either end but it would still only transcode sometimes. I discovered that my backend would sometimes try to run the transcode job on my slavebackend and that is when it would give error 242. If my slave backend is down transcode runs on the master backend and works great. I don't know if that was why my R5D1 +.20 install failed randomly. ???

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R7.4 Master Backend/Frontend 1 Ceton InfiniTV 4 AMD x4 9850/4GB/nVidia210 60GB SSD 5x2TB RAID5
Slave Backend/Frontend 1 Ceton InfiniTV 4 AMD 1050x6/4GB/NVidia 9500 40GB SSD 2x500GB SATA Maxtor
(Can't get 2nd Ceton tuner to work)

Does anyone know how to keep transcode jobs from running on the slave backend or how to make the slave successfully run them?

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R7.4 Master Backend/Frontend 1 Ceton InfiniTV 4 AMD x4 9850/4GB/nVidia210 60GB SSD 5x2TB RAID5
Slave Backend/Frontend 1 Ceton InfiniTV 4 AMD 1050x6/4GB/NVidia 9500 40GB SSD 2x500GB SATA Maxtor
(Can't get 2nd Ceton tuner to work)

I was having this same problem according to the mythtv wiki this error is from trying to transcode with a slave backend. I managed to get around this by mounting /var/lib/mythtv/recordings on my slave backend.