Smack: service-unavailable(503)

I keep gettings stacks like:

service-unavailable(503)
at org.jivesoftware.smackx.filetransfer.FileTransferNegotiator.negotiateOutgoingTr ansfer(FileTransferNegotiator.java:407)
at org.jivesoftware.smackx.filetransfer.OutgoingFileTransfer.negotiateStream(Outgo ingFileTransfer.java:300)
at org.jivesoftware.smackx.filetransfer.OutgoingFileTransfer.sendFile(OutgoingFile Transfer.java:123)

I am usig a fully qualified to: address, for example: "testuser@test.server.com/Smack". I havent found any settings for the Smack API to set a file proxy (shouldnt matter, everything is running on one box). I get identical results with both Pidgin and Spark 2.5.8, so what am I not configuring at the Smack end of things?

I can chat happily, its just file transfers that fail. the transfer line is:

fTransport.sendFile(fullyQualifiedTo, “Captcha.jpg”,data, “Reply with the capatch phrase to ensure you aren’t a bot.”);

Clues please?!

Duh, should have mentioned, using Openfire 3.6.0a

And so, yes it is smack related, just not where I was expecting. Its not related to the connection, its indirectly set:

FileTransferNegotiator.setServiceEnabled(xmppConnection,true);

for anyone passing.