[plaur]

What is the proper alert when I playing online at BBO, forget our system and open 2♦, with a hand consistent with a weak 2 in ♦ , when our agreements firmly are that 2♦ is both majors, Ekren style?

Should I alert my 2♦opening bid:
a) weak with both majors, could be 4 -4
b) I have a weak 2 in ♦, but our agreement is weak with both majors
c) anything else

[guido]

You are required to tell the opponents your agreements, not the hand you hold.

Agreements are both explicit and implied,however. If you "never" forget agreements with your partner of the moment (i.e., she/he has no reason to think you have anything other than a weak major two-suiter) than a simple explanation of the agreement suffices. If, however, this partner knows you forget agreements, you need to let the opponents know that also.

[blackshoe]

There is of course the problem that you can hardly explain an agreement you've forgotten. OTOH, if you remember (after you've given an incorrect explanation) you're supposed to 1) immediately call the director and then 2) provide the correct explanation. 1) rarely happens in f2f bridge, much less on line.