According to the log:
2018-05-05 10:57:39.945 INFO SCRIPTING: 10095( 10652)/E: DATABASE00003._RegisterGroupTemplate({[1]=Group,[2]=a,[3]=Coalition,[4]=1,[5]=Category,[6]=2,[7]=Country,[8]=0,[9]=Units,[10]=a,})
2018-05-05 10:57:49.921 ERROR DCS: Mission script error: : [string "a:Spawn()..."]:1: attempt to index global 'a' (a nil value)
[string "a:Spawn()..."]:1: in main chunk