This only happens when the customer or who ever has the files has not got the version of the software your using....
They either need to upgrade to 2 2 software which they can do by going to here
Silhouette - Download New Software
Or the designer needs the first software that was brought out... I always use the first version of the software as everyone can then open my files as they are forward compatible...
Also to take into consideration is if the designer is using the designer version of the software and used features that the customer does not have in their basic version they also won't be able to use.