Rear camera shutter closed after screen replacment.

After replacing the LCD screen and digitizer on a 4S, the camera app shutter remains closed and I'm unable to swith to the front camera.

I've ensured all parts are correctly in place and connected to the logic board. I've double checked all the teardown/reassembly guides on this site and other sites and everything is in the correct place.

I've tried 3rd party camera apps, when using 'Snapchat' the rear camera fails to work but the front facing camera does work.

I've also tried the 3rd party torch app, this doesnt work.

I replaced the rear facing camera with a different rear camera. The same problem remains. I installed the original camera into a different 4S and it worked fine. So its not a problem with the actual part.

I've done the all the software resets that have been suggested on this site as well as other sites, to no avail.

Does anyone know of any camera connections issues or issues with the camera short circuiting? I replaced the tape that was originally in place and the small rubber square that sits under the rear camera is in place.

I've trawled the internet for an answer, i'm hoping there is someone on here who can help.

Many thanks

Adam