'Wrong forward reference' and unresolved symbols between adjacent files

Hi,

I'm just trying to use IDEA as the editor for some Scala code files already in existence here at my office. I have never written Scala before nor used IDEA for Scala, though plenty for Java.

To do this I used 'New Project', selected Scala with SBT and created the project within the existing code directory. Note that the file structure around the code is like
project/
|
| - a/
  | - A.scala
  | - B.scala
| - b/
  | - C.scala
| - c/
  | - D.scala

First problem: in any file whenever the code references a class later in the file IDEA shows a code error "wrong forward reference". Ok actually it's often an object, not a class.

Second: In directory a, for example, where there are multiple scala files. The code often references classes in adjacent files in the directory. But every time IDEA shows a code error 'Cannot resolve symbol <class or method name>'.

Any advice? I think the IDE is using the Scala that I installed via Ports which is 2.10.