Multiple differing results need to be highlighted with a formula...

Hi. I need some help...

I have a spreadsheet that I need a little help on. Attached is the sheet. All data has been changed and is hypothetical.

Imagine a world where seperate parts of the microsoft office package need a seperate part serial number to access. ie word needs its own license. but i have two same licenses and they are linked to both excel and word. oh no. this must mean i have corrupt data somewhere... i need to identify where the duplicates are and highlight them for further investigation.

Can you have a quick looksee at my sheet and tell me if you can help with a formula to identify i have an issue...

Or if you can think of a better way of identifying my problem.

As you can see, the green are not erroneously linked to multiple products, but the grey are. I cant think what i could use to highlight this without looking thru manually...

thanks very much in advance,
t