Could be a number of things. The flashing etc. is an indication of a fault present. Unfortunately it isn't clever enough to display what it is.
You could hook up a PC to the data link of the LPG ECU
to see what's going on or go through a couple of visual checks to see if you can spot something.
Can you hear both solenoids working when it tries to switch? The solenoid at the front may be difficult to hear as I seem to remember that it had to be mounted low at the front as the traction control system was in the way of where I would ideally have mounted it. You could test for low pressure gas at the small flexible pipe which connects from one injector block to the pressure sensor. Gas should be around 1.5 bar on the low pressure side.
Check that the flexible hoses are OK especially the two smaller diameter lines to the pressure sensor.
Check the wiring at the 2 thermal sensors have not cracked as they enter the sensor body. One on one of the injector blocks and the other mounted on the vaporiser.
That's about it of the common problems.