Main switch works, remote switch will turn light off but not on

Has it always been this way or have you recently replaced switches? Regardless, this is typical of the 3way switches being wired incorrectly. One of the travelers and the common are swapped. If you changed the switches it is important that the wires go back on the correct terminals. NOT NECESSARILLY THE SAME PLACE ON THE SWITCH AS THE OLD ONE. The wire that went to the brass screw on the old switch (common) should go to the Com. screw (brass)on the new switch. The remaining 2 wires (travelers) should attach to the remaining screws. Doesn't matter which, just 1 wire to each screw. Both switches should be wired the same way.