you need to burn them correctly
Insert a blank CD into the CD writer.
In the File menu, select "Burn CD image".
Choose as file type: all files (*.*), since Nero expects files with the NRG suffix.
Select the ISO image file.
You will see a dialog box asking if you want to supply detailed image parameters. Enter the following parameters:
Type of image: Data Mode 1
Block size: 2048 bytes per sector
File precursor and image trailer: 0 length
No scrambled and no Swapped.
Click on "burn". If the program complains that there are errors in the image file, click on the button "Ignore" and launch the burning.