As Sub hasn't been able to look at my files yet, I'd also add the fault also happened tonight after I updated the EPG manually. So I wonder if it's something to do with that?
After changing my anti virus provider, there has been some improvement with this issue. However I had to set the programme again just after 1700 for it to work without having to reboot the PC.
More testing today. I didn't record before 1700, which is usually BBC News HD on COM7, before recording Channel 5 HD on PSB3/BBCB 5pm. Today the C5 HD recording worked.
So I think it's something to do with the COM7 configuration is mucking up NDigitalHost.exe.
4.1.0 seems to have resolved this issue. Did a test recording of BBC News HD on COM7 from 1600-1658 and now Channel 5 HD (BBCB) at 1700 and it's recording.