Assigning aircraft to route

[Airfox]

I am unable to assign my aircraft to a new route. Going round in circles. Please advise.
Airfox of HollandAir

[Aoitsuki]

explain:

what did you do(procedure)
weather it is a new route, a route from/to where, aircraft used.

what error did you get

[Zombie Slayer]

Agreed, more explanation needed.

Couple ideas, did you create the route for the correct aircraft type? (Sounds dumb, but I have done it) Is the aircraft you are trying to schedule at the same base as the route?

The path is Routes -> Scheduling -> Green + at far right of the desired aircraft -> Select desired route to add -> Click OK -> Apply maintenance checks.

[JumboShrimp]

As the other reply says, you go at it the other way.  Instead of assigning an aircraft to a route, you assign the route to an aircraft (or more precisely, to the aircraft's schedule).