I am in the same boat. My phone is rooted and has no bloat but it took the Kit Kat update. Now that the knock code update is out, it won't let me take the update. I get the "suspected of rooting" error message too. Only difference is I am running some Xposed modules.
I disabled my Xposed modules but left everything installed. Rebooted and attempted the update again. Still the same problem.
Then I uninstalled Xposed and all its modules and still the same problem.
If you find out how to take the update, please up date this post so the rest of us know how as well.
Originally Posted by XxZombiePikachu
Have you removed bloat/modified the system(xposed/mods) If so then you have to put everything back to stock
Sent from my LG-D800 running stock kk, rooted with philz using XDA app