Since this hasn’t been resolved (at least not on this forum), I’m going to bring up something presumably similar:
MacBook Pro mid-2012, 2.9 GHz i7, MacOS 10.11.6
Parallels Desktop 11.2.0 with Windows 7 Professional (6.1, Build 7601)
Adobe Experience Manager (AEM) Designer 18.104.22.16850517.1.919161
Boxcryptor 2.3.401 (733)
When I try to open a PDF with AEM Designer (via double-click, Open command, or drag & drop) from an encrypted Dropbox folder (i.e. from the Boxcryptor volume), it won’t open, instead AEM Designer shows the error message “Wrong Parameter” and/or becomes unresponsive.
Opening the same file (to be precise: a copy of it) from a Dropbox subfolder (obviously unencrypted) with any of the methods mentioned above works just fine.
Thank you for hints and ideas.