[MP2]

You're setting his health to -20, not curHealth-20. Plus you can't have multiple statements after each case in a switch, and && isn't used for multiple functions on a line..

pawn Код:

case 4:
{
    new Float:curPlayerHealth;
    GetPlayerHealth(playerid, curPlayerHealth);
    SetPlayerHealth(playerid, curPlayerHealth - 20);
    SendClientMessage(playerid, COLOR_YELLOW,"You have been hurt while mining metal.");
}

Also 'You have been hurted' isn't proper English. 'been' is past tense (as opposed to be and being) so you don't need to say 'hurted' (past tense also). Also you're using SendClientMessageToALL..