I fixed it myself, even HIKvision tech support couldn't fix it. Let me explain...
So if you install the latest version of the ivms 4200 software and you connect it to DS-KT804EF access points, if you don't upgrade the firmware of the access point it will give you an error because the way the new software stores fingerprint data is different to previous versions.
Now you have to pay close attention to this small detail. First check the firmware version you are running, if it is 1.2x then you can download the latest version and install it remotely then reboot and you are good to go.
If you are running a firmware version 1.1x then the latest version will not work, the device will enter into an eternal reboot cycle and then you have to upgrade the firmware via usb. The firmware version you need to use is 1.1.3build190311 this version is the only version in the 1.1x series that is compatible with the new format of fingerprints that the ivms4200 v.3.11.1.7 uses.
HIKVision say that the latest version of the firmware works fine if you are upgrading from 1.1x but you should not reboot after update, what you should do is save the configuration file before you upgrade and then import the configuration afer firmware upgrade. It did not work for me. I in both situations, rebooting afterwads and not rebooting resulted in the eternal reboot loop.