I haven't seen that error yet, but we're still determining if DMX is a good fit for our company. You might want to try upgrading to version 3.4.10 (log into snowcovered and go to "My Account" for a list of upgrades).
03.04.07
Fixed bug where FileType edit caused file type to be destroyed
Rewired some response redirects in an attempt to get rid of ThreadAbort exceptions
03.04.08
Fixed error when Auditemail is specified and not message is sent upon action (e.g. import)
Fixed bugs in Custom attributes and date handling in attributes
Set the Url creation in the notifier to use HostUrl & Default.aspx to avoid any issues with child portal notifications
03.04.09
Bugfix in addon settings screen error. Check now on module's FolderName for core or not. This will allow DMX friendlyname renaming and rebranding.
Bugfix to make extension list localization more robust.
New import mechanism for admin. Solves any timeout issues with big imports and the code is more robust.
Subscriptions possible again on root collection of an instance
Fixed download filename with spaces problem for both FF (ignored part after firt space) and IE7 (replaced spaces with underscore)
Fixed bug: Admin now no longer gets error when viewing private content
03.04.10
Fixed bug where custom attributes would no longer be read due to new way to name controls in DNN 04.05.01.