Toolbox has internal limitation to evaluate imports of nested packages. Assume there is a file defined following:

package foo
package bar

class Foo {
  def bar = "bar in Foo"
}

and usage in other file

package acme

import foo.bar

object Main extends App {
  (new bar.Foo).bar // <- BREAKPOINT HERE
}

Let us stop now in BREAKPOINT HERE and evaluate

val a = 42

Expression Evaluator context looks like following

{
  import acme._;
  import org.scalaide.debug.internal.expression.context._;
  import org.scalaide.debug.internal.expression.proxies._;
  import org.scalaide.debug.internal.expression.proxies.primitives._;
  {
    import foo.bar;
    {
      val __this: acme.Main.type = JdiContext.placeholder;
      import __this._;
      {
        val a = 42;
        ()
      }
    }
  }
}

And error:
Compilation failed
object bar is not a member of package foo