I get a status 7 error without having rooted my device, what do I do?

[AC Question]

I get a status 7 error without having rooted my device

I have an HTC One m8, not rooted. The update to Android 6 is available since last week. I've tried installing it 3 times, each time I get the same error (see log below). I did a softreset, then even a hardreset, but even after that I get the exact same error. Like I said, I made no changes whatsoever to my device.
Here's the log (copied it manually while stuck in HTC's useless tech support. I suspect a few single letters are missing, it looked like some text spilled over the right side of the display):

E:missing bitmap oem_unlock_bg
(Code -1)
E:missing bitmap oem_unlock_bg_yes
(Code -1)
E:missing bitmap oem_unlock_bg_no
(Code -1)
Finding update package...
Opening update package...
Verifying update package...
Installing update...
M60QCT.01.002.018
mount: failed to mount /dev/block/platform/msm_sdcc.1/by-nae/userdata at /data: Device or resource busy
Verifying current system...
E:unknown command [set_err_msg]
"/system/media/audio/ringtones/Daffodil.flac" has unexpected contents.
E:Error in /data/data/com.android.providers.downloads/app_fta/OTA_M8_UL_SENSE70_MR_HTC_Europe_6.12.401.4_R-4.16.40.13_release_464427.zip
(Status 7)

Installation aborted.