I do not understand what noksagt means with it is more "fragile".
the file is then synchronized in the zotero folder in dropobox on pc B, but you don't see it as a zotero item in zotero library.
Unfortunately I am a technical naive and I don't fully understand noksagt's explanations.
Moreover dropbox seems not able to sync the sqlite file.
Since you don't seem to be very earnest regarding the possible marriage of dropbox with zotero, which other provider(s) of online storage would you recommend?