Lines in Logo

Had a customer send me their logo to put on tshirt. I cleaned up the graphic and changed into a pdf so that could create the transfer in my Icolor500 machine. The logo looked great. However when tried to print the transfer the graphic had very thin black lines in 3 places on the transfer. They did not show on the screen in corel draw. So I went back into corel draw and created a color box-copy-pasted and moved over into the box to see if they showed and they did as long as I was moving the graphic but then were invisible again when landed it in the colored box. I'm not a graphic designer so I don't know how to erase them when they are virtually invisible on the computer screen but show up on the image print transfer. Can anyone help?