Because NCryptoki is a wrapper to the underlying PKCS#11 module, the errors depends on such a module.
Anyway I think that in your case the problem is that you set two conflicting attributes:
template.Add(new ObjectAttribute(ObjectAttribute.CKA_TOKEN, false));
template.Add(new ObjectAttribute(ObjectAttribute.CKA_PRIVATE, true));
You set CKA_TOKEN false, i.e. the key must not be stored in the token and CKA_PRIVATE, i.e. the key must be kept private
try to set CKA_TOKEN to true,