Your itinerary is valid
OSL-xLON-NBO-DOH-MLE-KUL-HKG-LAX-HEL-OSL
As you pointed out, the online tool has its issues; and the error message you are getting is spurious.
I managed to price up your itinerary using the tool:
Base Fare: NOK57,959
+++: NOK17,467
TOTAL: NOK75,423
The trick to getting it to price was to specify the first segment as OSL-NBO