The presented study is a commentary to the judgment of the c. Erlebach of 17 May 2018. The main interest of the Author has become only one thread of this the Rota’s judgment, which is the problem of retroactivity of the can. 1098. In this judgment, ponens argued for the origin of this regulation from positive law, and therefore its non-retrocativeness. In the final remarks, the Author highlighted the specificity of the arguments Rota’s auditor. In his reflection over can. 1098, based on both dogmatic and comparative analysis, showed that the error resulting from deceptive action is not a substantive error, but an accidental one. Therefore, in his opinion, can. 1098 comes from positive law.