Am getting lots of errors in my spamtrain log, excerpt below.

Anyone have a hint as to what might be causing the exception ? Bad message ? Bad index of some sort ?

Training Snapshot:
zimbra TP: 50 TN: 29 FP: 1 FN: 1 SC: 0 NC: 0
SHR: 98.04% HSR: 3.33% OCA: 97.53%

Overall Statistics:
zimbra TP: 499 TN: 343 FP: 85 FN: 50 SC: 0 NC: 0
SHR: 90.89% HSR: 19.86% OCA: 86.18%
dspam_clean starting
PROCESSING USER: zimbra
Processing sigs; age: 14
Processing probabilities; age: 0
Processing unused; any: 90 quota: 30 nospam: 15 onehit: 15
20130108230115 Finished dspam training
20130108234502 Starting spam/ham cleanup
[] WARN: exception occurred fetching message
javax.mail.internet.ParseException: Expected '=', got "null"
at javax.mail.internet.ParameterList.<init>(Parameter List.java:247)
at javax.mail.internet.ContentType.<init>(ContentType .java:114)
at javax.mail.internet.MimeBodyPart.updateHeaders(Mim eBodyPart.java:1331)
at javax.mail.internet.MimeMessage.updateHeaders(Mime Message.java:2107)
at com.zimbra.common.zmime.ZMimeMessage.updateHeaders (ZMimeMessage.java:343)
at javax.mail.internet.MimeMessage.saveChanges(MimeMe ssage.java:2075)
at javax.mail.internet.MimeMessage.writeTo(MimeMessag e.java:1770)
at javax.mail.internet.MimeMessage.writeTo(MimeMessag e.java:1749)
at com.zimbra.cs.util.SpamExtract.writeAttachedMessag es(SpamExtract.java:379)
at com.zimbra.cs.util.SpamExtract.extractMessage0(Spa mExtract.java:349)
at com.zimbra.cs.util.SpamExtract.extractMessage(Spam Extract.java:296)
at com.zimbra.cs.util.SpamExtract.extract(SpamExtract .java:245)
at com.zimbra.cs.util.SpamExtract.main(SpamExtract.ja va:194)

Thanks in advance