Build 15007 won't install

I am on 14986 with my Lenovo Ideapad Miix. Never had problems by upgrading the insider previews in the past.With the latest 2 releases (15007 (and 15002 too) I experience the following. Download very slow. It shows 0 % for 1 hour, then 100 % for another hour, then asks to restart; upgrade procedure seems to work fine until the end, then GSOD and after the restart I find that the installation rolls back to 14986.I tried every solution found on google, but failed. In the GSOD for a few seconds I can read something like "Security check failure..." Cannot upgrade to new releases anymore? Sorry for my terrible english.

3rd party app interfering maybe.

GunnzAkimbo: I even tried starting from a fresh new 14986 without external apps.

AndreTen: Yes, I did. And there is more than enough space. Plus, I removed all usb devices, SD, , external peripherals, etc.
Terrible is that the upgrade from 14986 to 15007 takes hours and hours (last time more than 5 hours), only to tell you at the end that it rolled back to 14986...

mine didnt take hours, about 2 hours total (download and install).

Thanks AndreTen.
No antiviruses, no external apps, enough space on HD.
I installed a clean 14986 preview. Let Windows to chose the needed drivers. then tried again to updated to 15002 (failed again with a GSOD at the end of the procedure, this time 4 hours after the beginning of the download), and tried with preview 15007 without success. Used all available tools on 14986 (windows update troubleshooter, drivers check, etc.). Every tool finds no problems on my machine. Tried to disable the default UUP without success. It seems that the problem only affects the 2 latest relases. I installed older releases without problems.

15007 is a bit rough.
Im finding the nvidia driver crashes when multitasking.

Thanks GunnyAkimbo. I am now downloadin the iso of 15002 for a clean install.
If it goes wrong, will I be able to roll back to my 14986 or the clean install deletes old versions? I ask this because I don't have a 14986 iso, and have only one notebook. If it goes wrong and I cannot roll back...

cant do rollbacks when clean install, it installs whatever build you install and thats it.

I would call 15007 a "friday build" (fix it on monday attitude).