Complicated - Errors/Dropdowns

I have attached the excel file. Please read it as on the page it describes exactly what needs to be done.

Here is what is written on the page. (Very complicated so any help is appriciated)

How do I make it so that A's can clash, but B's cannot clash if they have the same option for A on the drop down menu. Eg.

A = Option A
B = Option C
A = Option A
B = Option D

or

A = Option A
B = Option C
A = Option B
B = Option C

are both fine

but if

A = Option A
B = Option C
A = Option A
B = Option C

occurs then both option C's show up as red.

This has to work across all drop down boxes and only the two that are wrong can go red.

Then for the special option, I want it to be so that no matter how many times and how its selected they never go red.

Thanks

P.S Any explanation will be appriciated as I will be doing it with varying amount of drop boxes.

Thanks for your time

Cheers,
Tom

Thanks I will try this. May be a little complicated as I have Dutch Excel. Will get back to you. Thanks for your time.

Hate for it to be to much to ask, but would you mind putting it in the excel sheet and attaching it once you have put in the formulae. This way excel automatically and correctly changes the language of the coding because I tried to translate it myself and it gives an error code.

I managed to get it to work but it does not do as I wanted it to. Thanks ! Anyone else please really need help

Cheers, Thomas