What is the typical error of a voltage follower opamp
With two voltages (input, output) I would expect that it is likely a "voltage follower".
More than that, are you sure about the part number?

When speaking about classical voltage opamps the real closed-loop gain for the unity gain amplifier (follower) is 

\$Acl = \dfrac{Ao}{1+Ao}\$  with Ao: Open-loop gain.

Fort a typical value \$Ao=10^5\$ (100 dB) we have 

\$Acl = \dfrac{10^5}{1+10^5}\$ which is very close to unity.

However, it is to be noted that the open-loop gain Ao continuously decreases with rising frequencies and causes - in addition - phase deviations. Hence, we have Ao=Ao(jw). 

However, each opamp has an input offset error between µV (very good devices) and some mV (universal types). This voltage is amplified with unity and, thus, appears with the same value at the output. But it is not an amplification error but a fixed dc shift of the operational point.