IMPORTANT
From May 7th HMRC no longer accept RTI, CIS Submissions or Sending of HMRC messages for the following operating systems:
Windows 7, Windows 8, Server 2008, Server 2012 or 2012R2.
If you use any of the above, to continue to send HMRC submissions, you will need to upgrade your current operating system or move the payroll to a computer with Windows 10 or later. Moving payroll to a new PC
This is due to security upgrades that are incompatible with the listed older versions of Windows. There are no workarounds, IRIS Support can't help as HMRC are not accepting the submissions.
Windows 10 and 11 will continue to work.