Just how I would look into this.

1. Google. Example:
http://www.google.com/search?hl=en&q=vb6+crash+excel+protected+sheet

2. Read the first hit.
"If Sheet1.ProtectionMode = True Then
'UserInterface
ElseIf Sheet1.Protection.AllowEditRanges = True Then

End If" is in the example to see if the sheet or ranges are protected.

3. Using that information I could alter my code to check if the sheet is protected and bail out.

Remember it's your code. You are the author so you get to find where you crashed.

Bob