[mattydr67]

First of all what vauxcom 160115a do you use?
Are you using vauxcom 120309a+160115a?
Or real vauxcom 160115a?
First one is for china cline and it is a fake
Second one was for HQ clones.
What 170823c EN are you try to use?
There is one for original or china clone and one for HQ clone.
So as example for you to understand better.
If your tool is in Hq clone mode and you are using vauxcom 160115a for HQ clone ( of course) and you are trying opcom 170723c EN for original or clones you will have the error that you describe and viceversa.

To be sure what kind of tool you have ( in which mode it is ) you can use OCflash. When you are trying to see to flash it you will have an warning message before flashing that will warn you that you are in HQ clone mode if your tool is in Hw clone mode.

About how to calculate that  bits for Hq clones mode I don't think there are many that can do it. 
Good luck