]Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,7)
I have my new Pi 3 set up the way I like and decided to make a duplicate SD card as a backup.
I created a disk image using the Unix terminal dd command on my Mac and appear to have created a disk image . I then reformatted a second sd card and using the reverse operation in terminal appear to have copied this backup.img with two partitions onto the SD card. Everything appears to be right. The new sd card has two partitions "boot" and "RECOVERY" as expected - but!! when I put the duplicate card into my Raspberry Pi I get the Kernel panic error message shown above during the boot process.
I have tried running the disk repair utility on the duplicate card with no success.
The duplicate card has only 16 G while the original card has 32 G, but only a small fraction of the space is used and therefore should fit.
I would greatly appreciate some advice - thanks