Did you replace it with the one I mentioned? And did you ground the wire coming out of it to a verified good ground?
I'll give you the run down here. A flasher is built to recognize when a light is burnt out. It does this by sensing the electrical load passing through it. LED bulbs require much less power, therefore much less load. When you install LEDs, the stock-type flasher senses too little load and lights the signal up solid (or makes it flash faster in newer cars,) to warn you that a bulb is out. Because of this, you need to add resistance to the circuit. There are many ways to do this, but if you have too much resistance then you won't have a warning when a bulb is out. If you don't have enough resistance, you will still have a solid turn signal. Because of this, it's easiest to use an LED compatible flasher, because it takes all the guesswork out.
So, saying that, does your turn signal light up solid? Or nothing at all? If it lights up solid, you have a resistance issue and NEED this flasher, no question. If it doesn't light up at all, then you have a bad connection somewhere. Could be the switch, although very unlikely at this point. You will need to do some hunting with a voltmeter.
Or just give up and put incandescent bulbs back in.