For the last week or so I have been periodically getting this dialog popping up, shown below. It would seem from googling around that this is related to Google Drive.
I have tried the recommendations on Apple Support Communities, specifically I have used the Browse button on the popup and selected FinderSyncAPIExtension by going to the finder and opening Google Drive > Show Package Contents > Contents and dragging FinderSyncAPIExtension.appex into the Browse window. That did not resolve the problem. I have also tried deleting Google Drive and installing it fresh from Google.
Currently, after I get this popup (and cancel it), GDrive stops syncing and I have to quit it and start it again to get it to start syncing again.