I have a user that just had OpenRoads updated to 10.10. Only has a few files that would get hung up on transcode or something like that and then crash. He is able to open those files in 10.09 just fine.
Here is the exception file.
/cfs-file/__key/communityserver-discussions-components-files/5922/1614.exception.log
The other user has both installed. I wouldn't think that would be a problem.
You might think about uninstalling both versions of the product, and reinstall 10.10 only (if 10.9 is not needed and everyone is upgrading anyway). Make sure that you delete the old directories while you are at it.
Mark
Forgot to mention that another user that was just updated to 10.10 is able to open those files with 10.10.
Just a quick thought... have the dgnlib files been updated to this latest release of the software?