MemcachedKeyCharacterError: Control characters not allowed

[amxku]

Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/tornado/web.py", line 1141, in _when_complete
callback()
File "/Library/Python/2.7/site-packages/tornado/web.py", line 1162, in _execute_method
self._when_complete(method(*self.path_args, **self.path_kwargs),
File "/www/v2ex/galaxy/handlers/web/system.py", line 39, in get
self.aa()
File "/www/v2ex/galaxy/handlers/__init__.py", line 443, in aa
aa_count = self.mc.get(aa_key)
File "/Library/Python/2.7/site-packages/memcache.py", line 898, in get
return self._get('get', key)
File "/Library/Python/2.7/site-packages/memcache.py", line 847, in _get
self.check_key(key)
File "/Library/Python/2.7/site-packages/memcache.py", line 1062, in check_key
"Control characters not allowed")
MemcachedKeyCharacterError: Control characters not allowed