there are a lot of poss reasons... but since it was working fine before, it could be on the receivers end or you could have an ip mismatch would be my first guesses. Check by typing /dns yournickhere and //say $ip and compare the two, if they arent the same, try typing /localinfo -u
you could also check:
file/options/general/lock to be sure you didnt disable sends make sure you didnt put the person on ignore
try /remote off in case its a new script messing things up
try a different server port to connect to the network
