It appears that it is not possible to delete a project if it is in a certain state. The error message though is not very helpful:
javax.jdo.JDOUserException: One or more instances could not be deleted
NestedThrowables: javax.jdo.JDODataStoreException: Delete request
failed: DELETE FROM PROJECTDEPENDENCY WHERE PROJECTDEPENDENCY_ID=?
NestedThrowables: SQL Exception: DELETE on table 'PROJECTDEPENDENCY'
caused a violation of foreign key constraint 'PROJECT_FK2' for key (40580). The statement has been rolled back.
We had a process that seemed to be stuck. We tried then to delete the project but this only caused the error message above. I believe that Continuum could not delete the project because it was in a state that does not allow deleting it. If this is the case I would like to suggest to provide a better error handling letting the user know why the delete failed.
We finally could delete the project after we restarted Continnum (not sure if this was necessary, but that is what we did) and then building the project again. This time it went through and after the build was successful, we could delete the project.