I went through something similar to this recently (I ended up being fired, now have a lawyer and several complaints lodged)

If they have given you this warning, they cant use it to dismiss you! They have to prove that the error was a sackable offence and also that you did not make an effort to fix the problem (If there even is one!)

Contact the Human Rights Commission as well, if you believe they are setting up a way to dismiss you and take away your entitlements, they can help you lodge a complaint.