Does it crash regardless of which vessel you switch to/from? Does it crash when you load up the default "DG and DG-S" scenario and switch vessels?
In any case, it is likely that one your installed add-ons is the problem. I recommend a standard troubleshooting approach:
1. Install a clean copy of Orbiter to a new directory.
2. Load up one of the default scenarios and try switching vessels.
3. If that works, install one add-on and repeat your test.
4. Repeat step 3 until the failure occurs; that will pin down the problem add-on.
The key is to install one add-on at a time and re-test after each one is installed. Then once you locate the problem add-on you can either try to manually uninstall that add-on from your main Orbiter installation or you can create a new Orbiter installation that does not have the problem add-on installed.
It is also possible that one of your add-ons is configured incorrectly (or is missing a dependent add-on), and that is what's causing the crash. In any case, the first step is to figure out which add-on is causing the problem.