"It is not possible to work with this colleague."
Translation:S touhle kolegyní není možné pracovat.
Colleague can be masculine or feminine, it should accept "s tímhle kolegou" as well.
And, what a surprise, it is accepted.
If some particular sentence was not accepted, you really have to report the complete sentence. Duolingo has the "My answer should be accepted" feature for this very purpose.