[RESOLVED] Invalid Property Value upon Word 2003 form reset

My apologies if I'm pushing my luck by posting 2 questions in one day, but I've been trying to resolve this problem for a while now and keep hitting a brick wall.

On my Word 2003 userform, I have a series comboboxes. All of the comboboxes are set .Matchentry = True, although .Listindex = -1 for some and .enabled = False for others (these are enabled and populated by preceeding choices). I also have a reset button. When the rest button is pressed, all comboboxes are set to = null and the ones that were originally disabled are disabled again.

My problem is that once the reset button has been pressed, the user is stuck in that section of the form until new values are entered into the comboboxes! If the user tries to select another part of the form or another page, a MsgBox appears with "Invalid property value". And, sometimes, the user can't even enter a new value because when when the drop down arrow is clicked the error message appears (I have been stuck a few times and had to terminate the form using the red cross). Don't know if this is anything to do with it but the disabled comboboxes were enabled, a choice was made and then they were reset, i.e cleared and disabled.

I have tried to resolve by setting combobox.value = "" instead of null (don't actually know the difference). I have also tried combobox.Listindex = -1 rather than null or "" - neither seems to fix it.

As always, any help is greatly appreciated.