Sorry I wasn't clear. I actually tried the code using the asmData provided with ScalismoLab. I previously ran the code using the asmData images that I converted to float using 3D Slicer, but I went back to the provided data to remove that potential source of error.
Here is a link to a GitHub gist with the code I used. I copy and pasted this entire code into the editor of ScalismoLab using the asmData provided with it.
Building Active Shape Model from ${imgAndMeshFiles.length} training data...
datasets\asmData\mri\19.vtk, datasets\asmData\faces\19.stl
java.lang.IllegalArgumentException: requirement failed
at scala.Predef$.require(Predef.scala:212)
at ASMBuild$.surfaceToTransform(<console>:194)
at ASMBuild$.$line35$$read$ASMBuild$$trainingDatum$1(<console>:168)
at ASMBuild$$anonfun$makeTrainingData$1.apply(<console>:182)
at ASMBuild$$anonfun$makeTrainingData$1.apply(<console>:182)
at scala.collection.Iterator$$anon$11.next(Iterator.scala:409)
at scala.collection.Iterator$$anon$12.nextCur(Iterator.scala:434)
at scala.collection.Iterator$$anon$12.hasNext(Iterator.scala:440)
at scala.collection.Iterator$class.foreach(Iterator.scala:893)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1336)
at scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:59)
at scala.collection.immutable.VectorBuilder.$plus$plus$eq(Vector.scala:732)
at scala.collection.immutable.VectorBuilder.$plus$plus$eq(Vector.scala:708)
at scala.collection.TraversableOnce$
class.to(TraversableOnce.scala:310)
at scala.collection.TraversableOnce$class.toIndexedSeq(TraversableOnce.scala:300)
at scala.collection.AbstractIterator.toIndexedSeq(Iterator.scala:1336)
at scalismo.statisticalmodel.asm.ActiveShapeModel$.trainModel(ActiveShapeModel.scala:46)
at ASMBuild$.main(<console>:276)
... 30 elided