"Buddy Addition failed" = contact was added locally, server cannot add such contacts because they are removed from the ICQ system.
but whose history and contact in my list has gone missing.
restore from the database backup if it exists
if not, say thanks to Mail.ru Group (the ICQ owner) for the fact that it began to delete inactive accounts from system...
for our part, we did everything we could - added a fix so that Miranda would not erase contacts from now on