Ttrying to abbreviate name in a cell

Hello,
Im trying to abbreviate a name in excel cell but it wont abberviate it giving the message that the value entered is not valid, a user has restricted values that can be entered into this cell.
first i used data validation to equal 6 characters or less then highlighted cells that do not match the criteria

example
Matthew Hernandez
Kathleen Adams
Mary Thompson
Sharon Mitchell
Lawrence Taylor
Howard Sanchez
Theresa Baker
Kevin Barnes
Louis Griffin
Tammy Moore

cirlce names above 6 letters and abbreviate them but it keeps giving me that message , does it have to do with data validation or cell formatting
thanks for the help

I dont know what you mean. What part do you want to abbreviate?
Do you simply want "Matthew Hernandez" to become "Matthe" ? (this can be done with =Left(A1;6) supposing A1 contains the name

hi...what i want is this in the image...i have the D column and i want the final result like in F column...is this possible?Sem Título.jpg