Whenever I attempt to launch a game it kicks me back to the main menu and says "A serious error has occured" and to check the forums (shown above).  This is the first one Diagnostics - 2019'01'28 @1526'05''.html.  After this I checked the integraty of the files and it said everything was fine, so I started up the game again and it happened Diagnostics - 2019'01'28 @1604'00''.html and I tried again and it failed again Diagnostics - 2019'01'28 @1609'17''.html.  

I had a bunch of mods when this first occured so I thought they might be affecting it so I untinstalled all of them and it happened again Diagnostics - 2019'01'28 @1611'26''.html.  At this point I thought that if I uninstalled and reinstalled the game it would fix it but unfortunetly it failed again Diagnostics - 2019'01'28 @1622'27''.html.  Then I tried again just to see if closing it and steam would help but unfortunetly it didn't Diagnostics - 2019'01'28 @1624'16''.html.

Here is my DxDiag: DxDiag.txt

Output Log: output_log.txt

Thank you for looking at my post.

I would try to delete whole documents/Endless Space 2/ folder then verify integrity of game files and restart game. Or - perhaps better - wait for an official answer.

Keep in mind to copy your save files in another place before deleteing folder above - in case you like to keep them.

Checking the Diagnostics files, I am met with a wall of errors pertaining to the sandbox mod. Could you try completely uninstalling (rather than just disabling) the mod and get back to us with information on whether the issue persists?

That error is likely that the mod is not installed but there is a custom faction that uses its traits

tsunamic did you ever get a response in regards to this? and if so what were your options and did they work?

Reason being is I am currently suffering the same dilema as you and i've also deleted all custom factions as to people's issues with them.