(i) Error of law or erroneous interpretation cannot be excused
In J 3/88 the Legal Board noted that account should be taken of the fact that under Art. 134(1) EPC 1973 the contracting states had in principle confined representation of applicants before the EPO to "professional representatives" who, by virtue of their qualification should guarantee the best possible representation. The Legal Board stated that it followed that a representative could not relieve himself of responsibility for carrying out tasks which, by reason of his qualification, fell upon him personally, such as, for example, the interpretation of laws and treaties. If he delegated such tasks to an employee and if the latter made an error in the course of that work which resulted in the failure to observe a time limit, the representative could not claim that he had taken all due care required by the circumstances (see also J 33/90).
In J 31/89 the Legal Board confirmed that erroneous interpretation of the EPC owing to a mistake of law on the part of the duly authorised representative with regard to the rules for calculating time limits (in the case in point, regarding the late payment of a renewal fee together with the additional fee) could not be excused. The appellant and the representative failed to determine correctly the last date for valid payment of the renewal fee (see J 42/89, T 853/90, T 493/95, T 881/98, T 578/14).
In T 516/91 the board considered that by mistakenly believing that an extension of the time limits set by Art. 108 EPC 1973 was possible, the representative had failed to exercise due care (see also T 248/91, T 853/90, T 316/13).
According to T 316/13, a European patent attorney is expected to know the EPC provisions concerning the legal remedies available in the event of failure to observe time limits, even if he has never been faced with the problem before, without waiting for the board of appeal to tell him exactly what he needs to do.
(ii) Exceptions to the rule that an error of law or erroneous interpretation cannot be excused
In T 624/96 the board expressed doubts about the nature of the original mistake, which concerned calculation of the time limit for filing the statement of grounds of appeal. This was possibly a "mistake of law" caused by ignorance or misinterpretation of the provisions of the EPC, as in e.g. J 31/89 or T 853/90. The board found that in the circumstances of the case at issue, however, the agent had not made a "mistake of law" of this kind. The agent cited an earlier appeal in which he had represented the same applicant, showing that he indeed had some familiarity with the appeals procedure. He also submitted programmes of training courses, at which he had given talks on European patents and EPO proceedings. It could be therefore be ruled out that a legal error in calculating the period for lodging the statement of grounds of appeal might have arisen from his ignorance of the EPC.
In J 28/92 the Legal Board held that the misinterpretation of a provision of the EPC by a representative was not without basis or unreasonable and considered that there was no basis for penalising the representative for having arrived at a not unreasonable interpretation of a rule of the EPC, which subsequently turned out to be wrong. The representative's interpretation of a legal provision of the EPC was not the result of, and did not lead to, a failure to exercise all due care required by the circumstances. In T 493/08 the board shared the view expressed in J 28/92 and stated that there might be exceptions to the rule that an error of law could not be excused, which, however, could be acknowledged only under rigorous criteria.
In J 13/13 the Legal Board confirmed that an error of law could be excused if rigorous criteria were met, namely where there were genuine doubts and differences of opinion as to how a provision was to be interpreted. Such doubts and differences of opinion could be considered legitimate only if, after scrupulous attempts to clarify the matter, including by reference to the boards' case law, the right interpretation remained objectively unclear and the view later found to be erroneous was reasonable.