Operation failed is known issue and now you will also get it while opening games or app folder. And only solution for this is re-flash, it happened with my k810 also and only re-flashing sorted out the issue. Master reset, updating using SEUS will not work.
And flashing is pretty easy using XS++ and use ver 1.6 or above for k800. Go thru any tutorial for flashing you only need Main, FS and custom pack.
hope this helps.
hizzzzzzzzzzzzz
rattlesnake