We have new tax return software this year - yes, we had to cope with that on top of the Covid 19 issues, its been quite a year so far. We have been finding in a good 10% of the CT600s that when we go to file the CT600 that the IRMark has changed on the software so no longer agrees with the signed declaration from the client. Our software provider has advised that this is due to the "HMRC Schema (which is applied behind the scenes)" which changes the IRMark. But they have stated it isn't important becase HMRC do not look at the IRMark . What do other people think of this? It is really frustrating and is tempting me to return to our much simpler rturn software we had before.