Hi Paul,
It sounds to me that you’ve got Outliner open. We strongly recommend that you never have Outliner open when using PlusSpec as it will slow your computer down and most likely make SketchUp crash.
If that doesn’t fix the issue would you be able to please take a screenshot of the information that appears in the Ruby Console when the issue occurs? To get this information open the Ruby Console (go to Window > Ruby Console) and then recreate the steps you took to get the issue. If nothing appears I would recommend trying the following and see if that makes any difference when changing windows/doors.
Also, the plugins you mentioned shouldn’t be clashing with PlusSpec.
I look forward to hearing back from you.