timemachine error by filevalult

hi guys i am using my MacBook 2016-13inch 251gb 8gb ram with touch bar - high Sierra

I bought wd MacBook hd 1tb so I back up my data and some weeks gone and now

I tried to back up one more time but when i try to back up my MacBook shows me this problem

I think in English it says

time machine can not complete back up.

time machine doesn't back up because FileVault is encrypting disk or diencrypting disk so when Filevault complete its work time machine will start backup

but i checked FileVault in english

Filevault is turned on for the following disks 'kapin'

pls! help me guys....