Is it EzDok v1 or v2?
For EzDok v2, check the exe.xml which (if P3D is installed in the D:\) can be found at C:\Program Files\ Lockheed Martin\Prepar3D v4\exe.xml
Open the .xml with notepad and find:
<Name>EZdok camera addon2</Name>
<Path>C:\Program Files (x86)\EZCA2\ezlauncher.exe</Path>
If it isn't there, add it. If it still doesn't work, try adding it to the other exe.xml which can be found at:
C:\Users\<your name>\AppData\Roaming\Lockheed Martin\Prepar3D v4\exe.xml
Try adding it in that exe.xml. (If it isn't already there.)
Also, try try reinstalling EzDok v2 (with your antivirus off, although I never had problems with Windows Defender.)
If you have Ezdok v1, I recommend reading this EzDok guide posted here in AVSIM: (However I don't remember if EZCA v1 was able to communicate with P3D v4)
Also, the post above is mean't for P3D v3, however, I don't think you'll have a problem with this, as I think EZCA is not fully compatible, but compatible to some extent with P3D v4.
Of course, I stopped using EZCA about 8 months ago, so sorry if I don't know how to fix this because I always hated EZCA's bugs and problems. Try upgrading to ChasePlane. I know it isn't an option for everyone, but when you have the chance, ChasePlane is so much better.
But please mention your EZCA version. I don't remember seeing EZCA v1 being compatible with P3D v4.
This guy uses EZCA v1, and I guess it is compatible, but you need to create a fake Prepar3D v3 roaming folder for the EZCA Configuration tool to work. (IF you're using EZCA v1.)