Are there more details provided in the error message?
What version of the game do you have? (shown below the buttons in the main menu; 1.0.40 is the current version)
So this is with the single player or multiplayer campaign? Can you start a skirmish (single or multiplayer against AI)?
For the Steam version, try starting the game directly, rather than using the Steam shortcut. In Windows Explorer, browse to the install folder below and double click on the program file
..\SteamApps\common\Divinity Dragon Commander\shipping\DCApp.exe
There is a preview branch of the game for Steam where you can get early access to not fully tested patches (instructions
here). There is currently a preview for the 1.0.55 patch available, though it may not have any impact on your problem.
Please email supportdc@larian.com, with a description of the problem and the report.zip file generated by the
Dragon Commander support tool.
[FAQ] Troubleshooting Dragon Commander & support