When I double click on a pdf file in a Directory Opus folder, it usually opens in Acrobat 11. However, there are times when it will not and Acrobat 11 displays a Fatal Error message "Acrobat failed to connect to a DDE server". To open the file I have to use Acrobat, and it will open the file. I use a stand alone laptop with no network, running Windows 7 64 bit, SP 1. Can you advise why this might be so?
Does the same happen in Windows Explorer? This sounds like an Acrobat issue rather than an Opus one.
This thread on Adobe's forum may help: Acrobat failed to connect to a DDE server