Thank you for your post.
FileMaker Pro 11 uses the labels installed in the Labels folder inside the FileMaker Pro 11 folder. If you are in the United States, make sure the Labels folder contains the file LabelsUS.flb. If not, then open the "Labels (Inactive)" folder, make a copy of the LabelsUS.flb file, place the copy into the "Labels" folder, and rename it to LabelsUS.flb.
If the file is already there, create a new database file, and try to create a new Label layout. If this also fails, quit all applications, relaunch FileMaker Pro and see if you are able to create a Label layout. If this fails, then I would reinstall FileMaker Pro 11.
Keep me posted with any progress.