The Plus icon is disabled because 1:1 Operations Manager allows only one open standard revision in the CDH standard release at a time. In this lesson, that usually means a standard revision was already created earlier, so the system will not let you create another one. Open the existing revision in the CDH standard release section and continue the exercise in that same revision. Once that revision is completed or no longer open, the Plus icon becomes available again. This matches the training guidance that revisions are managed through Revision Management and that only one revision can exist for a release at one time