GL-MT300N-V2 Transmission - Tracker gave HTTP response code 503 (Service Unavailable)

I have set up Transmission and it is working though the web interface. Problem is that for one particular tracker I have several torrents seeding but only one is active. All the others return the message “Tracker gave HTTP response code 503 (Service Unavailable)”, and are not seeding.

Has anybody come across this?

Sorry, I don’t understand your question. Can you give me more information?