I just tried it and had no problems (otherwise I would probably have had them before and fixed them
).
The access violation you get came because the verdata editor is for verdata not for tiledata
Verdata.mul was some kind of patch format EA/OSI used to update client data. It can contain several different types of content (nearly everything of the other mul files). I implemented that mostly because I still use the verdata as a format for patch transfer. (As you probably noticed, MulEditor includes the option to create a SFX Verdata Patcher - that means, that it "converts" a verdata.mul into an executable which can patch the content of the verdata back into the original mul files, so it is easier for admins to distribute new content even to clients above version 4.0.5b).
The instructions of the first post are more or less outdated, as they still use the verdata editor. You can directly edit a tiledata entry if you double click it on the right side (in the "Mul files"-tree). When you change something there and hit "ok", it should already be saved. The same with art, gump, etc.
You can test it by double clicking the same entry again and you should see the updated info (or you just close the editor and look ingame
)
If there is still trouble, let me know