It could be that the backup is looking for the same disk format. Supposedly SD media does not have physical boundaries, however, experience with some cards and some readers (like
here) leads me to believe otherwise. Therefore if the backup software did the backup at a low level it could be expecting the same "physical boundaries" to exist :roll: .
To work around this, you could get a card reader, copy the data to your computer, then copy it on to the new card. I have used this method in the past with no problems.