A false judgment; a discrepancy between the mental judgment and the object of this judgment.
Error is different from ignorance, although it implies ignorance and proceeds from it.
Ignorance implies lack of knowledge without the formation of a judgment; error can occur only in the presence of some knowledge, and expresses a mistaken judgment.
If the error concerns the existence of some particular fact, it is factual; if it regards a precept of law, it is legal.
It may affect either the substance of a thing or its quality.
A substantial error exists in the case of one marrying other than the intended person, or, where slavery is legal, of a freeman marrying a slave.
Error in such cases is a diriment impediment to matrimony.
Such a substantial error, if proven, nullifies any ecclesiastical act.
An error of quality or accidental error does not itself annul the act, unless expressly stated in the law.
The law protects common error concerning jurisdiction.
New Catholic Dictionary