Issues using SvnVcs from custom plugin

I'm new to Intellij plugin development and this is my first post here, so I first wanted to say 'Hi' to everyone.

I've got a problem using SvnVcs from within a custom plugin I am developing and I was hoping someone could help out with it.

When I try to use the class after adding it to the Intellij SDK I get a ClassNotFoundException.

However, if I switch the jars to be libraries on my plugin project, I get the following error:-

org.jetbrains.idea.svn.SvnVcs cannot be cast to org.jetbrains.idea.svn.SvnVcs

Can anyone tell me where I am going wrong please?

Thanks in advance!

Andy