The problem can happen when you are trying to install/reinstall MacOS and FileVault is active but optimizing is not yet completed.
Go the Recovery mode (hold cmd + R during boot)
– open a terminal, and type:
diskuitl cs list
In the Logical Volume you will find
Conversion Progress : Paused
– I opened a second terminal window
– Searched for the binary ‘corestoraged’:
find / -name 'corestorage*'
– found it in the recovery folder:
– Started corestoraged in the found folder:
– Check the HD via the first terminal, the Conversion progress now showed a percentage, after a hour the hd was converted.
– than I could reinstall El capitan from the same recovery mode.
– After the reinstall everything was like it was.