SinBad

If you are playing from steam, first move your mod folders somewhere safe for a moment (anywhere but the ksp directory). Then from your steam library, right click on ksp and find 'check file integrity' or something similar. If i recall, its under the options selection of the right click popup.
That will scan your ksp folder and replace any missing files.
When its done, move your mods back in.

Top left of the building window in vab or sph is an arrow. Click it and the palete moves over to reveal all sorts of new tabs, including sub assemblies.