I started a new six-sided box in Vcarve and believe I corrected the problem as well as found the source. Although I have not cut it out yet as I am waiting on new bits, the computer model in VCarve Pro looks promising.
Here is what I learned when designing a six-sided box. The creation of the dovetail joints on a six-sided box must be done in the following sequence.
#1 Create the dovetails on the tops and bottoms of the sides FIRST
#2 Create the pins in the top and the bottom SECOND
#3 Only after the top and sides THEN create the dovetails in the sides
#4 Finally, create the pins in the sides
After I successfully cut the next six-sided box using the dovetail gadget, I will then post an update with photos.
The above sequence is missing from most online videos and tutorials.