Zotero cannot communicate message can occur with browser connector, or when citing in Microsoft Word, Google Docs, or LibreOffice/OpenOffice.
Try this first:
Ensure the Zotero desktop app is open on the computer. In our experience this usually solves the communication error for downloading pdfs using the browser connector. If not, please contact us.
If Zotero is already open and you are trying to cite in a Word document:
Go to Zotero > Tools > Add-ons.
Disable the Word plugin.
Close Zotero (cmd + q on Macs).
Open Zotero and return to the Add-ons menu.
Enable the Word plugin.
Close Zotero (cmd + q on Macs), then open Zotero again.
Close Word (cmd+q on Macs) and open it again
Zotero desktop "not responding" at pdf import
When you import more than one (or a single large file) pdf to the Zotero desktop app, sometimes the program will stop responding or display a "Not responding" message in the program's menu bar. Leave the program alone and let it finish importing. The more files you import, the longer it will take for the program to respond.