Can't save subassembly "THE SELECTED PART IS NOT ATTACHABLE!"

When trying to save a 'science prob' (see below image), I keep getting the above message and can't save it.

Action taken to produce result: Build the module (see image), drag and drop the OKTO pod to the 'drop zone'.

What might be the reason and can it be saved?

Solution 1:

You can't save full (component-wise) ships as subassemblies. Basically they need to be parts of a ship, where the piece you save from (the piece you click and drag over to the subassemblies section) has to be a piece that connects multiple pieces together, like a stack separator/decoupler. I'm not sure that you can have any kind of a command probe or module in a subassembly.

Solution 2:

You definitely need to re-root to the engine where you're attaching (probably a launch vehicle). I ran into this when making a combination of lander and tanker. The lander lands with nearly no fuel on the mun, but launches a tanker to transport fuel and kerbals back to the lander if needed. But now you'll have a mun base that can transport fuel to any similar designed lander (and if you made your mun base correctly, can practically make fuel at will.).

Once I re-rooted to the poodle engine, I was able to save it as a sub-assembly called lander_tanker. I'll let you know my success when I put it on the mun in career mode.