Tape door won't shut and message C:31:40

You need a qualifier Tech trained from Sony to repair your CAM
Your problem is that the cassette compartment it had 2 sensor and a few contact to detect what kind of tape you are insert like normal, metal or Digital 8 or Hi 8 or 8 Standar or cleaning tape so the system control would auto adjust according the tape
Those contact conducted by flexible cable now that FC may be cut or the sensor faulty when you insert the tape the CAM detected 1 side of the tape so it juded like some thing wrong with the tape then it will not load the tape in because it designed to protect the tape and protect mechanism
Without the tape no problem because the sensor or contact at the right corner of CAM did not detect any thing
If You want to know how it detect what kind of the tape, just turn the D8 tape up side down, you can see the holes on the left and right corner where is the tab for save and record
You need to replace 1 chassis LS assembly it cost about $250 to $350 if you are in AUSTRALIA
I hope that give you some ideas