Estou usando o SBT0.13.1.

projeto / build.properties é o seguinte:

sbt.version=0.13.1

Executandosbt about imprime o seguinte:

$ sbt
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[info] Loading project definition from /Users/jacek/sandbox/so/sbt-0.13.1/project
[info] Set current project to sbt-0-13-1 (in build file:/Users/jacek/sandbox/so/sbt-0.13.1/)
[sbt-0-13-1]> about
[info] This is sbt 0.13.1
[info] The current project is {file:/Users/jacek/sandbox/so/sbt-0.13.1/}sbt-0-13-1 0.1-SNAPSHOT
[info] The current project is built against Scala 2.10.4-RC1
[info] Available Plugins: com.typesafe.sbt.SbtGit, com.typesafe.sbt.SbtProguard, growl.GrowlingTests, np.Plugin, net.virtualvoid.sbt.graph.Plugin, com.timushev.sbt.updates.UpdatesPlugin
[info] sbt, sbt plugins, and build definitions are using Scala 2.10.3

Com a seguinte tarefa -hello - nobuild.sbt:

scalaVersion := "2.10.4-RC1"

lazy val hello = taskKey[Unit]("An example task")

hello := {
  print("Sleeping for a sec...")
  println("done.")
}

...ereloadrelatórios sbt[error] Type error in expression:

[sbt-0-13-1]> reload
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[info] Loading project definition from /Users/jacek/sandbox/so/sbt-0.13.1/project
/Users/jacek/sandbox/so/sbt-0.13.1/build.sbt:6: error: type mismatch;
 found   : String("Sleeping for a sec...")
 required: sbt.TaskKey[String]
  print("Sleeping for a sec...")
        ^
[error] Type error in expression
Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore?

Quando eu mudoprint paraprintln a tarefa está definida corretamente.

Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore? r
[info] Loading global plugins from /Users/jacek/.sbt/0.13/plugins
[info] Loading project definition from /Users/jacek/sandbox/so/sbt-0.13.1/project
[info] Set current project to sbt-0-13-1 (in build file:/Users/jacek/sandbox/so/sbt-0.13.1/)
[sbt-0-13-1]> hello
Sleeping for a sec...
done.
[success] Total time: 0 s, completed Jan 4, 2014 10:31:43 AM

Éprint não aceito na definição de tarefa?