I was getting the unresolved dependencies like the question here.
Getting org.scala-tools.sbt sbt_2.9.1 0.7.7 ...
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SBT 0.7.7 uses Scala 2.7.7 for the project configuration. SBT 0.11 uses Scala 2.9.1. You can use SBT 0.7.7 for configurations up to that version, but versions of SBT newer than 0.7.7 use a non-compatible configuration file.
Note that this is not related to the Scala version that will be used to compile the project itself, just the Scala version that is used to compile the configuration file. These are different things: you can use whatever version of Scala you want to compile your project, but you must use the version of Scala mandated by the SBT version to compile the project configuration.
To get an error message like that you must either have changed the Scala version for the project configuration, or used a newer SBT with a project written for an older version of SBT. Find out which it was, and correct the problem as needed.
I have an SBT 0.7.7 for projects that have not yet migrated to the new version, and the latest SBT for everything else. Put a different name on each script, and you are good to go.