problem with manifest file importing snapshot

I have two sites a and b... both have snapshot pro installed both point to same dropbox default folder...
I backup a, chcked and backup is there on dropbox folder
In b I cannot see this backup

so I try to import it into b ... I go to dropbox, grab the link and paste it into b import.. start the import and i get

PHP max_execution_time: 900s

Attempting to download remote file:

Processing archive: (139.53kb)
Error: Manifest data not found in archive.

Snapshot import complete

what is happening? tried this twice .. exactly the same

please advise