I have for about a year I have been using firmware and driver version ZEDR_16V3.5.5.10185 with no problems.  Recently updated to version ZEDR_16V4.1.0.14624 and am now getting lots of audio dropouts.  Even increasing buffers or changing the driver from 56 to 258 or higher still results in dropouts.  Anyone else see this?  This only relates to Allen & Heath ZEDR-16 mixers.
 
The dropouts seem to only be with Sonar.  I am running Sonar X2a Producer on Windows 7 Pro.  Using the console via firewire for other programs seem to pose no problems.  IE; iTunes, Youtube, Adobe Audition, Windows Media, etc.

I reverted back to the 3.5.5.10185 version.  And back to having no problems.  Still waiting on answers here and from Allen & Heath support.

After discussion with Allen & Heath technical support, they think it is a Sonar issue.  I argued that it is only a problem with the updated firmware+Sonar combination.
 
I have submitted this to Cakewalk support for advice and am waiting on a solution.
 
I am hoping maybe someone here with a similar setup might be having the same problem or maybe yours worked.  I would like to know this also.