SbtJsTask throws an Exception

[pme123]

When running sbt run I get this exception (after loading http://localhost:9000):

[error] TypeError: less.render(...).then is not a function [error] at C:\opt\dev\examples\play\play-scala-websocket-example\project\target\less\lessc.js:152:18 [error] at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:380:3) [error] [error] at com.typesafe.sbt.jse.SbtJsTask$.$anonfun$executeJsOnEngine$1(SbtJsTask.scala:218) [error] at scala.util.Success.$anonfun$map$1(Try.scala:251) [error] at scala.util.Success.map(Try.scala:209) [error] at scala.concurrent.Future.$anonfun$map$1(Future.scala:287) [error] at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29) [error] at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29) [error] at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60) [error] at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:140) [error] at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) [error] at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) [error] at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692) [error] at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157) [error] (web-assets:less) com.typesafe.sbt.jse.SbtJsTask$JsTaskFailure: C:\opt\dev\examples\play\play-scala-websocket-example\project\target\less\lessc.js:152 [error] .then(handleResult, handleLessError); [