A trial of the service at Euston Station, which was to begin next Monday, has now been put back until the end of June.
DHJ is in negotiations with another company to take on the running of the XTP project. The other XTP consortium members - Viacom, London Underground, Citylink and the cable company Thales - have put the launch on hold until DHJ's problems are sorted out.
The delay follows problems with the technology itself, which had already seen the Euston test put back. However, Viacom said these teething problems have now been ironed out.
Problems with the roll-out of XTP have frustrated advertisers such as Nestle and Virgin Mobile, which had already worked campaigns across the XTP network into media schedules for June. However, Viacom is working on offering alternative space on the bus and tube networks.
XTP's business development director, Alison Reay, said: "Understandably there are frustrations with campaigns already planned for June, but we are looking at the situation and working on an early autumn launch."
Viacom is still able to take options for space, but cannot specify exact transmission dates to advertisers.