I use Scala 2.10.0RC1 and sbt 0.12.1. What causes and how can I fix this runtime error (runs fine on 2.9.2)?

The exact error message is:

java.lang.NoSuchMethodError: scala.Predef$ArrowAssoc$.extension$$minus$greater(Ljava/lang/Object;Ljava/lang/Object;)Lscala/Tuple2;

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