Even though the view that there is no ultimate truth is intimately connected via atheism to the denial of God, such a view is clearly self-contradictory. Such is the illogic of atheism. A self-contradictory belief is an erroneous belief, as is atheism.
To know that disorder exists, one must have an idea of order.
To know that someone is blind, we must know what it means to have sight.
When a sceptic tells you that there is no such thing as truth, or that you are in error regarding your belief in God, that same sceptic is refuting h/her own premise that there is no such thing as truth. For when a sceptic says that Christianity is false, that same sceptic is telling you that s/he is in possession of truth even while telling you that truth does not exist.
Atheism, self-contradictory, absurd, incoherent and illogical to the core.