[Darren69]

A failed coil stick would causee the bike to run on one but won't give you an error though so there is something else going on could be the crank sensor not sensing the timing marks correctly. I've just looked in the workshop manual and all it says is this:

PICK-UP
The pick-up used is the inductive
type. The engine pick-up is facing
the timing gear and can read the 46
teeth and the slot of 2 teeth.
The signals coming from the pick-up
are used by the control unit to
acquire the engine RPM and as a
timing reference.
Note
To check these components,
use the “MATHESIS” tester.

I though there was some shimming which you could adjust the position of the sensor with but it does not mention it.

Have you tried removing the sensor and cleaning it and the connector plug?