Sync error of the link.
This error happens when I open Zotero with the same account in two different PC at the same time. I have two laptops in both of which I installed Zotero and dropbox, target a folder in dropbox source-folder, and make setting same. I linked all of my files to the parent items in Zotero, thus I can open the files linked to Zotero in both of laptops without problem. The problem is found in the condition when I open Zotero in both PC at the same time. With opening Zotero in 'A' PC, in 'B' PC I linked some files to their parents item. In 'B' PC, I can open such linked files to click their parents successfully. But I cannot open same files in 'A' PC though I sync the data. After sync, when I tried to open same files in 'A' PC, Zotero in 'A' PC cannot find those files. How could I resolve this error?
You could use Zutilo https://addons.mozilla.org/en-US/firefox/addon/zutilo-utility-for-zotero/ to see where the links are actually pointing?