half tones not working!!!

Please bare with me as I am self learning in what I have done so far. I use corel draw for screen printing. I am trying to learn the 1/2 tone fade process and then venture into the 4 color print process. I am having problems printing 1/2 tones. Here is what I know and have done to start with.

I have a brother 7860dw laser printer. I have post script functions. and I can open the advance settings in the separations section and alter the  screen angles and frequencies. If I don't change nothing  it will print . I can change the angles and frequencies it still prints but when I try to set the 1/2 tone type to  anything other than the default it will spit out an error : undefined offending command load stack with some numbers and dashes. From what I have read on line from screen printers I need to be using an ellipse 1/2 tone type pattern for better results in the burning of the screens when I get to that point.  Though I have not tried to burn a screen using the default settings of the 1/2 tone type it looks like I am going to have a hard time picking up these dots or what ever shape the default is set on. I really don't know what the printout should look like when it is correct  but I was expecting to see more light between the dots I set the frequencies to 45 and added 7.5 to all the angles using the 4 color process colors. This seems to be and average rule of thumb by what I understand in the screen printing world, unless I am missing something. I can tell you that it is making a fade from one color to the next but there is hardly no light between these little dots