autolearn=unavailable

[fchan]

Hi,
Can someone tell me what is the cause of these 
"autolearn=unavailable" messages and there is a possible solution. I 
get them occasionally but wanted to know why are they appearing. 
Below is a sample of the log:

Mar  5 11:42:27 s1 spamd[13422]: spamd: identified spam (110.5/8.0) 
for qscand:510 in 5.8 seconds, 927 bytes.
Mar  5 11:42:27 s1 spamd[13422]: spamd: result: Y 110 - 
BAYES_99,BODY_ENHANCEMENT,BODY_ENHANCEMENT2,BOTNET,DATE_IN_PAST_06_12,DIGEST_MULTIPLE,DOS_OE_TO_MX,FORGED_MUA_OUTLOOK,HELO_LH_HOME,INVALID_MSGID,,PYZOR_CHECK,RAZOR2_CF_RANGE_51_100,RAZOR2_CF_RANGE_E4_51_100,RAZOR2_CHECK,RCVD_IN_BL_SPAMCOP_NET,RCVD_IN_PBL,RCVD_IN_SORBS_DUL,RCVD_IN_XBL,RDNS_DYNAMIC,STOX_REPLY_TYPE,,URIBL_BLACK,URIBL_JP_SURBL,URIBL_RHS_DOB,URIBL_SBL 
scantime=5.8,size=927,user=qscand,uid=510,required_score=8.0,rhost=localhost.localdomain,raddr=127.0.0.1,rport=56164,mid=<[EMAIL PROTECTED]>,bayes=1.000000,autolearn=unavailable 


Thank you,
Frank