All incoming messages fromApp are being rejected

Thanks for the wonderful quickfixj, and thanks in advance for shedding any light on this.

When receiving incoming messages which conform to spec, my engine rejects all of them. It's the same problem with two similar but separate projects (a 4.2 & a 4.3) with errors like these:

(Message 3 Rejected: Tag not defined for this message type:64)
(Message 46 Rejected: Tag not defined for this message type:55)
(Message 32 Rejected: Tag not defined for this message type:647)
(Message 5 Rejected: Unsupported Message Type)

I have user-defined these problem tags, still same error. My user-defined tags work as per messages I send out.
I get the "tag not defined" or "unsupported message type" or "tag not found" errors depending on how I tweak the data dictionary, but always an error.

Again many thanks in advance,