Paid *A RTW allows backtracking within the 3 IATA zones (Americas, Europe/Middle East/Africa, Asia & Southwest Pacific). Your routing seems fine in that regard.

I presume you have the minimum 10 days duration, 3 stops over 24 hours, no more than one stopover in each city, etc.

It may just be the link between the tool interface and booking engine is down. Try contacting LH (who does the ticketing for the RTW tool) - if you give them the itinerary you want to ticket they should be able to do it manually or tell you what the problem is in terms of fare rules.