1. Open SVN Repositories View
2. Navigate to an ivy.xml file in a repositoy
3. Double click to open it
   Error: Invalid Input: Must be IFileEditorInput

Works for XML editors, Java editors, etc.
Workaround: Right click on the file and click Show Annotations (opens in a basic text editor) or Compare... (opens in the compare editor).

Adding the Open With option to the context menu would provide a more obvious workaround.