I know this is due to the 25th anniversary update but my mod is still failing to launch with this error and I'm not really sure what the cause is. I thought the last patch fixed most mods not launching.
I've tried disabling the Steam API and all the external .dll files I'm loading but no luck. Source code is at https://github.com/tschumann/basis if that helps. The issue is somewhere in client.dll anyway - if I get rid of my client.dll the game reaches the main menu.