In my experience, errors in mods can on occasion freeze up the game instead of crashing it. Thankfully this happened to me very, very rarely.
Could it be that the mod you try to run was made for another version of Diplo than you have installed?
Also did you try to activate it only once, or did the error persist on a second attempt?
Yeah I checked that. I've got Diplomacy v. 1.00. I'm trying to run Distant Stars for Diplomacy 1.00. Its the right version.
If you have "showErrors" (or something like that) set to true in your settings file, then a grey pop up window will come up each time an error occurs in the game...most errors occur while a mod is being loaded (or when the game is being started with a mod)...
You may have to hit the windows key or task manager or something in order to see the pop up window, but that's likely the source of your problem...
Note that some mods have "errors" that don't actually cause problems, but will still cause the pop-up to come up...you can just hit skip to get beyond those...
Hm alright. Sounds like an idea. I went ahead and set showErrors to true, then I started up diplomacy and clicked Apply Changes for the Distant Stars mod (all checksums matching ofc). These are the errors I got:
Text FileArchive missing Label.
File: C:\Users\Allen\AppData\Local\Ironclad Games\Sins of a Solar Empire\Mods-Diplomacy v1.00\Distant Stars (D) 1.00\GameInfo\Gameplay.constants
Line Contents: DamagePercentBonus:ANTIVERYLIGHT:Pirate 0.25
Except its not just there. No, the same error appears well past Line Number: 1000 all the way into effects until I was too tired to keep clicking skip or break lol.
Did I accidentally the whole thing?