Comment 3 for bug 72995

I can get this error as well.
Each time nano is used with sudo the permission for .nano_history is set to rw for owner. Problem is that the owner is changed from user to root.

Using chown/chmod on .nano_history to revert the owner of the file back to the user is only a temporary fix since the next time nano is used with sudo it will change these permissions back to the "faulty" ones.

I did this to get rid of the error message:
Edit /etc/nanorc and comment out "set historylog". This will of course disable .nano_history all together.