Thanks for the reply.
I downloaded the ZIP for Availability Suite, which contained two ISOs (VeeamBackup&Replication_126.96.36.1996.Update3.iso & VeeamONE_188.8.131.5201.Update3.iso). I've mounted up the VeeamONE ISO and then running setup.exe from there.
Am I going about this the wrong way then?
OK, so I've downloaded Update 3 for Veeam ONE at the bottom of the Downloads page, which is the ZIP containing the EXE you mentioned, this is working as expected.