Variant System Version OTA error

I recently flashed my HTC One M8 back to stock Android 5.0.1 and Sense 6, I also rooted my phone. Later I got a notification to upgrade to Android 6.0,after downloading it tells me I have an android "system version variant", and it won't let me apply the update. I've checked /cache for the OTA zip to flash using custom recovery but its not there... Please is there any solution to this problem.

I am using the unlocked version of the One M8.

Thanks in advance...

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