HTC One [M7] Lollipop update fails
Do the following and it will solve your issue (install correctly): Copy the zip file to pc form "Phone\Download\OTA_M7_UL_L50_SENSE60_MR_HTC_Europe_7.19.401.2-6.09.401.11_release_XXXX.zip"


Extract "firmware.zip" from OTA_M7_UL_L50_SENSE60_MR_HTC_Europe_7.19.401.2-6.09.401.11_XXXX.zip
Extract "recovery.img" from "firmware.zip"
Activate USB debugging on your device (if not already)
Reboot your device on bootloader. I believe holding down "Power" + "VOL+" will do it (if not google it). You can use ADB command as well. "adb reboot-bootloader"
install the recovery using ADB command "fastboot flash recovery recovery.img"
Now try to update once again form OTA and it will work.


To avoid redownload this large file:


Copy the zip file which you copied from Phone to phone\update.zip
Reboot phone to recovery
Apply Update from Phone Memory (As HTC one to not have external memory)
Choose the Update.zip file


I hope you get the idea even if few steps might be slightly off.

Thanks
Shurid