Using any of the following commands will output a incorrect string:
/w @p <text>
/tell @p <text>
/msg @p <text>
The feedback:
Player 'commands.message.sameTarget' cannot be found
This message is wrong in the first place, and not really a missing string, as 1.10.2 outputs
You can't send a private message to yourself!
I can confirm this, also happens when the selector is @a, optionally with a valid scoreboard value (like @a[score_test=1]).
While @p could produce an error, @a should work even with just one player.
Interestingly, /tellraw @p and @a works fine for me.