Chatters uses client-side savefiles with encrypted data to store user preferences. Occasionally, a user will be unable to join. Instead, they will be disconnected upon joining and the following message appears in data/saves/logs/log.txt:
BYOND Error: failed to parse savefile text at line 0 (reading '#'):
This is due to the client-side savefile. I assumed that this would mean that it was a corrupt savefile, but I wanted to verify. I received a corrupted one from HiroTDK and I cracked it open in two different non-BYOND savefile editors to verify that it was in fact corrupted. Much to my dismay, it wasn't actually corrupt (as far as the savefile format goes, at least).
So from here, the only way I can proceed is posting a bug report on the matter. The latest Chatters source, which exhibits the problem, can be found here. For convenience's sake, I've uploaded a working copy of Chatters along with the client-side savefile here.
To reproduce the issue, all you have to do is put 43410.sav into your KeyInfo directory and start Chatters.dmb through DS or DD. Hiro had this issue initially and I experienced it in a separate instance, then I took his savefile and was able to reproduce it myself.