The /wall feature does not work on large channels with many users (it seems this is limited to 50 targets at once) , ie:
13:54 ùíù ste_ Too many recipients.
13:54 ùíù DrAmA Too many recipients.
13:54 ùíù raven Too many recipients.
13:54 ùíù nofeah Too many recipients.
13:54 ùíù swift Too many recipients.
Looks like the server checking needs to be changed for ratbox et al.