AdAway on stock nougat- copying of host file failed

hello im getting the following message everytime i try and download the lists "copying of host file failed! please read help for more information"
ive just updated to the android 7.0 through the developer program, twrp custom recovery installed with root access build number NRD90M
just wondering what could be causing this and if i can do anything to try and fix it thanks

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