Validating repeated values, then bring the result to another cell

Guys, at the beginning I thought it was simple to do, but I couldn't make it happening.


I have a sheet that I organize where people will work at, I have many possibilities and I can use the same employee many times, unless he's already working at some other place.

I need to warn the user (paint in red, msgbox, or anything) that he can't use the employee again (at that date) becouse he is already working in other location at that exactly day. He can use hem another day. If I wasn't clear just look at the uploaded sheet.

Another thing is I have to bring the status for the employee sumarizing his activities for all month at cell E131. Just bring the status from all place he has worked.

I hope you can help me, could it be done just with lookup and data validation or do I have to use a conditional code in vba?