problem

java.lang.NullPointerException
at quickfix.Message.parseGroup(Message.java:600)
at quickfix.Message.parseBody(Message.java:569)
at quickfix.Message.parse(Message.java:480)
at quickfix.MessageUtils.parse(MessageUtils.java:148)

At that position in the code the result of extractField is NULL. This happens on parsing the message because the position counter is greater than the length of the message. Line 758 in Message.java:

if (position >= messageData.length())

This is expected in some cases when parsing groups.
However in this current problem it happened because there were problems with the message length and checksum which went undetected by the FixMessageDecoder.
The FixMessageDecoder checks if the message ends with a checksum, i.e. tag 10=xxx. The message in question ended with that information but the SOH delimiter before tag 10 was missing.