A black screen when calling any of the dialog boxes, it's always caused by another product, which is mistakenly trying to force itself as the most foreground window. The edit window it's likely there, but might have been covered by the other addon window.
GSX, of course, doesn't try to do the same (forcing itself on the foreground) like this other product is doing, because if every app tried to do it at the same time, it would cause a big mess in the Windows messaging system.
Online clients are just one example, but there might be other like that. Anything that runs in parallel to FSX, or that starts FSX by itself instead of having you starting FSX from the normal FSX icon.