Cancel the screen that is open in Steam trying to run the FixTimestamps.exe
Navigate to your steamapps folder in the main Steam folder and then open the "dc universe online" folder.
Example path on Windows 7 x64: C:Program Files (x86)Steamsteamappscommondc universe online
Open the LaunchPad.exe file and sign into your Station account (register for a new one if you don't have one, it's FREE).
Once logged in, this will launch the DCUO launcher, download any missing updates, and get you ready to play. Once the updates are applied, simply click PLAY. Launching from within Steam next time will work.
Cause of error:
I am not 100% sure on the cause of the error, but I suspect it has something to do with the recent updates not being applied to the Steam version. Bypassing the Steam launch let's the client get the updates and finish the install.