If an armature is present, but not active the group_select_mode defaults to WT_VGROUP_BONE_DEFORM, and throws an error because it can't find any active vertex groups. we're now checking to see if any bone is actively deforming before switching to WT_VGROUP_BONE_DEFORM (else defaulting to WT_VGROUP_ALL) Pull Request: https://projects.blender.org/blender/blender/pulls/112648