"I do not know their names."

[vam1980]

Nevím is given for "I do not know" but it's marked incorrect. What does that mean and what's the difference between nevím and neznám?

[A_purrfect_cat]

Have a look into the link mentioned in that related discussion:
https://forum.duolingo.com/comment/26390345

[LongFellow3]

i also would like to know this...

[ion1122]

It is probably the difference between knowing facts or abstract ideas on the one hand, and knowing (being familiar with) people, etc. on the other. Cf. the German 'wissen' and 'kennen'.