scalac: Cannot connect to compile server at localhost/127.0.0.1:3200

I have the same issue. It works as expected in IDEA 13, but I get this warning in IDEA 14 EAP.

I'm experiencing the same problem:

Ultimate 139.69.2 on Mac

I have the same problem - 139.144.2 - windows 7

This problem was fixed, but changes did not get to the eap branch yet. You can download a nightly build from this page:
http://confluence.jetbrains.com/display/SCA/Scala+Plugin+Nightly+Builds+for+Cassiopeia

Thanks!!! It's indeed working now.

Tried with Nightly 217 and 211 - with rc2, but It now fails with this error in the message-window. Proect is loaded via maven and is a mixed java/scala project:

Error:scalac: Error: Scala instance doesn't exist or is invalid:
    version unknown, library jar: C:\Users\mokj\.m2\repository\org\scala-lang\scala-library\Version(2.10.2)\scala-library-Version(2.10.2).jar, compiler jar: C:\Users\mokj\.m2\repository\org\scala-lang\scala-compiler\Version(2.10.2)\scala-compiler-Version(2.10.2).jar
sbt.InvalidScalaInstance: Scala instance doesn't exist or is invalid:
    version unknown, library jar: C:\Users\mokj\.m2\repository\org\scala-lang\scala-library\Version(2.10.2)\scala-library-Version(2.10.2).jar, compiler jar: C:\Users\mokj\.m2\repository\org\scala-lang\scala-compiler\Version(2.10.2)\scala-compiler-Version(2.10.2).jar

    at sbt.ScalaInstance$.slowActualVersion(ScalaInstance.scala:122)

    at sbt.ScalaInstance$.sbt$ScalaInstance$$actualVersion(ScalaInstance.scala:119)

    at sbt.ScalaInstance$$anonfun$actualVersion$1.apply(ScalaInstance.scala:32)

    at sbt.ScalaInstance$$anonfun$actualVersion$1.apply(ScalaInstance.scala:32)

    at scala.Option.getOrElse(Option.scala:120)

    at sbt.ScalaInstance.actualVersion$lzycompute(ScalaInstance.scala:32)

    at sbt.ScalaInstance.actualVersion(ScalaInstance.scala:32)

    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$.org$jetbrains$jps$incremental$scala$local$CompilerFactoryImpl$$getOrCompileInterfaceJar(CompilerFactoryImpl.scala:80)

    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$$anonfun$getScalac$1.apply(CompilerFactoryImpl.scala:44)

    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$$anonfun$getScalac$1.apply(CompilerFactoryImpl.scala:43)

    at scala.Option.map(Option.scala:145)

    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl.getScalac(CompilerFactoryImpl.scala:43)

    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl.createCompiler(CompilerFactoryImpl.scala:22)

    at org.jetbrains.jps.incremental.scala.local.CachingFactory$$anonfun$createCompiler$1.apply(CachingFactory.scala:24)

    at org.jetbrains.jps.incremental.scala.local.CachingFactory$$anonfun$createCompiler$1.apply(CachingFactory.scala:24)

    at org.jetbrains.jps.incremental.scala.local.Cache$$anonfun$getOrUpdate$2.apply(Cache.scala:20)

    at scala.Option.getOrElse(Option.scala:120)

    at org.jetbrains.jps.incremental.scala.local.Cache.getOrUpdate(Cache.scala:19)

    at org.jetbrains.jps.incremental.scala.local.CachingFactory.createCompiler(CachingFactory.scala:23)

    at org.jetbrains.jps.incremental.scala.local.LocalServer.compile(LocalServer.scala:22)

    at org.jetbrains.jps.incremental.scala.remote.Main$.make(Main.scala:65)

    at org.jetbrains.jps.incremental.scala.remote.Main$.nailMain(Main.scala:23)

    at org.jetbrains.jps.incremental.scala.remote.Main.nailMain(Main.scala)

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:483)

    at com.martiansoftware.nailgun.NGSession.run(NGSession.java:319)

Caused by: java.lang.ClassNotFoundException: scala.tools.nsc.Properties

    at java.net.URLClassLoader$1.run(URLClassLoader.java:372)

    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)

    at java.security.AccessController.doPrivileged(Native Method)

    at java.net.URLClassLoader.findClass(URLClassLoader.java:360)

    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

    at java.lang.Class.forName0(Native Method)

    at java.lang.Class.forName(Class.java:340)

    ... 28 more

That is now fixed. Thanks for the reporting!

"Cannot connect to compile server" still not fixed, though (in the latest 139.222.5 build).