[CP8L - ZONE Error]

Hi - I moved into my house about 18 months ago and the existing alarm system showed no sign of life.  Along comes the virus so I'm thinking it's a good time to try and get it fixed. After a bit of looking around, I bought a new CP8L control box, battery and panel. Disconnected the existing board, replaced and rewired everything up to the existing IR devices and the bell. After powering up, and entering the default engineer code I get a message that says 'cannot set zone 7' and then after entering the code again and the alarm going off, I get the !!!CHECK!!! zone 7 code. Having walk tested all 8 IR sensors I do get a red led from each sensor as it is activated. I can narrow down which IR is 'zone 7' based on where the wiring goes from the control box, but I cannot be certain which one it is. Ideally I'd like to fix the issue related to the zone but in the first instance I'd like to delete zone 7 to try and arm and test the system further - but I can't get past the initial menu options to access the delete zone option.  Any ideas?  Obviously, I'm a novice here... so grateful for any help!  Shall I just disconnect AZ7 +- wiring from the board?  Thanks - Matt