playframework 2.2 - Why does sbt fail with NoClassDefFoundError: play/Play$ in Play 2.2.x projects after sbt compile in Play 2.3 project?

Question

Once I run 'sbt compile' on a 2.3 play project, I can't use 'sbt compile' to compile any Play 2.2.x projects anymore. This is the error when I run sbt command.

[info] Loading project definition from /Users/macbookpro/playproject/project
[error] java.lang.NoClassDefFoundError: play/Play$
[error] Use 'last' for the full log.
Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore?

Answer 1

I just had this same issue. In my case I was using Play 2.4, but it's probably the same cause. I had run activator ui in my project directory accidentally. It created a project/play-fork-run.sbt file which is for activator support, but was preventing sbt from working directly. Deleting that file cleared up the issue and I can now use sbt again.