I had this problem when I was trying to use a brass stencil to emboss using my Wizard. Jerri Kay told me to put a piece of thin paper towel over the embossing plate and the cardstock on top of that before I ran it through the machine. It worked.
I have since put a piece of tissue paper on top and under the cardstock in the embossing folder and then run it through the machine. I don't know why, but the tissue paper stops the cracking.
Hope this helps
"I have not failed . I've just found 10,000 ways that won't work" --Thomas A. Edison