I came to Video Help to find the answer but didn't - well not quite.
I had been using WinDV for a few tapes in my Canon MV5i MC miniDV cam with no problem then came the error 'Cannot find DV output pin'
My solution was to remove the firewire driver, reboot the PC, let Win 7 find and reload the firewire driver.
Result no error message and WinDV working again.
I think what corrupted the driver was loading Adobe Premier 2. I have used this with no problems in the past.
I removed it and the firewire driver and WinDV worked again.

I couldn't use my Win 10 i7 desktop because the motherboard didn't have a spare slot for the firewire card and USB didn't work with the camera. So I had to go 'old school' and match the old camera to an old computer running old software which worked fine.