Image Checksum Error

I burned a cd from the bootcd.iso image from the ZEN 7 SP1 install.
Works fine, I just have to type in the IP address of the imaging server
or supply the diskette with settings.txt on it. Now when I used a few
apps to create a new ISO image with the settings.txt added, I get the
following error:
Image checksum error, sorry...

Now I have done this before with ZFD 4 and ZFD 6.5 and never had this
issue. I assume that when one adds a file, then the checksum doesn't
match anymore. Does anyone have a way around this as I don't want to use
a diskette in addition to the CD. TIA.