Eclipse "this compilation unit is not on the build path of a java project"

I can't get autocompletion to work in Eclipse.

I'm working on the project on svn. I set up the project in Eclipse by going into

File -> Import -> Checkout As a Project -> New Project Wizard.

I chose Enterprise Java Application. Everything seemed to work fine except instead of autocompletion working as I expected I got a popup dialog displaying the message

This compilation unit is not on the build path of a java project.

I've Googled it and everyone says that the project must be a Java project, but it is! What is the problem?

Update

The catalog structure on svn looks like this:

-Project_name
  -application
     -META-INF
       application.xml
       MANIFEST.MF
  +build
  +db
  +deploy
  +dist
  +lib
  +properties
  +script
  -src
     -META-INF
        someother.xml (datasource info)
        persistence.xml
        folder hierarchy with source files (should be package)
  -web
     some folders
          .
          .
     files
       .
       .
     -WEB-INF
        faces-config.xml
        jboss-web.xml
        web.xml
     build_win.xml

How do I tell Eclipse where the source files folder, application.xml, and other configuration xml files are?

When you have a multimodules maven project under a parent project, make sure you're not editing the file in the maven parent project.

What I did to make one of my projects to check out properly is by

1) Import your project from svn

      file-->import-->SVN-Checkout Projects From SVN

2) Find your Project and then in the "Check Out As" dialogue make sure you have the radio button selected "Check out as a project configured using the New Project Wizard"

3) Go through regular steps.

The wizard pulls the project properly and then setups your eclipse....

without using the wizard I find that all hell breaks loose.....

Hope this helps...

This is what was missing in my .project file:

    <projectDescription>
        ...
        <buildSpec>
            <buildCommand>
                <name>org.eclipse.jdt.core.javabuilder</name>
                <arguments>
                </arguments>
            </buildCommand>
        </buildspec>
        ...
        ...
        ...
        <natures>
            <nature>org.eclipse.jdt.core.javanature</nature>
            <nature>org.eclipse.m2e.core.maven2Nature</nature>
        </natures>
        ...
    </projectDescription>

I have this issue from time-to-time and often it's because the project wasn't marked as a java project. You can change this by going to the properties for the project > Project Facets > and selecting java. You may then need to properly configure that project, but this is probably part of the problem

I also had this problem after converting my java project into a maven project. I solved it as follows:

Right click on your project ->Project Facets -> click on Java, then Apply.