All FlashCopy mappings in a tree of connected mappings must be in the same I/O group. The FlashCopy mapping was not created because the source volume that you specified is the source or target volume in another FlashCopy mapping and the I/O group of the other FlashCopy mapping is different from the I/O group that you specified.
You have two options. The first option is to delete all of the FlashCopy mappings that contain the source volume that you specified where the FlashCopy mapping is in a different I/O group from the I/O group that you specified, and resubmit the command. The second option is to resubmit the command and do not specify the I/O group attribute. If you perform the second option, the default value of the I/O group attribute is used.