You will have to import the snapshot into a previous version of Designer 6.0 (i.e. 5.6m0, 5.6m1, 5.6m2) and then export the snapshot again using one of these versions.
Now you will be able to import the snapshot into series 6 of Designer.
Now you will be able to import the snapshot into series 6 of Designer.
UPDATED:
November 6, 2017