This can occur if, in your generated plugin.xml, there are multiple org.eclipse.ui.commands extensions with the same ID.
In my case this occured because my .gmfgen had two Gen Editor Generator > Context Menu items. Perhaps this is from a previous migration. Removing them ensured the error would not happen again.
I wrote this test case to check against existing gmfgen's to ensure this problem did not regress.
Error initializing element type "org.eclipse.gmf.tests.runtime.emf.type.core.employee": element type with same ID already exists.
These errors can be ignored. These errors come from the org.eclipse.gmf.tests.runtime.emf.type.core JUnit test plug-in, which can be removed from your launch configuration.
This occured when I upgraded to GMF 2.2.2. The problem is that I was adding an IFigure programatically to another IFigure without properly adding a new Constraint for the LayoutManager.
The solution was to add a new Rectangle constraint, as in r1740 of IAML. This also removed the requirement to add a LayoutListener.
This is a validation warning that you can ignore, but it is actually fatal. Trying to generate the diagram code from this .gmfgen will create an invalid line in XXXDiagramUpdater#getXXXSemanticChildren(), looking for a containment feature that doesn't exist.
The "Appearance" Tab in my generated GMF editor is disabled, but only for some nodes.
I can't change the colour or font of a label or node in my GMF editor.
If you specify your own Font style in a .gmfgraph, by default the generated .gmfgen will have "fixed font" set to true for this node, in Gen Diagram > Gen Top Level Node XXXEditPart > Inner Class Viewmap XXXFigure > Style Attributes.
If you set this to false, the font can now be modified. There was a request in 2007 to disable this "feature" by default.
I added an automated test to remove this in r2302 of IAML.
The EMF generateUUID() method can be slow on Windows NT-based systems because the random number generator is seeded by listing all of the files in your temporary directory; and if you are like me, your temporary directory is filled with tens of thousands of files. Try emptying your temp folder.
The destination of the plugin you are trying to generate may be out of sync with Eclipse. Try refreshing the plugin directory (F5).
Page updated 21 July 2011.