I downloaded this modpack recently and was adventuring, when all of a sudden it crashed to main menu and I believe it labelled OpenTerrainGenerator as one of the offending mods. Looking at the logs it mentions
Could not allocate the requested id 270 for biome Canyon. All available id's under 256 have been allocated. To proceed, adjust your WorldConfig or use the ReplaceToBiomeName feature to make the biome virtual.
I have no clue how to do either of those things. A full link to the log can be found here.
EDIT: I've used mcedit to change my character's position towards my spawnpoint and it is still crashing, labelling OpenTerrainGenerator.