hcitool lescan shows I/O error

Question

I\'m trying to do a lescan using hcitool on the raspberry pi.

The command prints out

Set scan parameters failed: Input/output error. 

Answer 1

It is possible, that HCI is currently in use. In my case I must stop Node-Red and it works. So take care, that the HCI isn't in use.

Restart the HCI is a way, to solve the problem temporarily, but it doesn't solve the problem right.