Language Explorer "flags" problematic environments with a red wavy underline (such as ). You may see this when you insert or edit one in a String Representation field, Environments field or Infix Positions field.
In Problems, the Records pane lists all the problematic environments (unless you deleted the problem report). The Text field gives a description of the problem.
Alternatively, right-click a flagged environment, and then select Describe Error in Environment. An information box appears with a description of the problem.
For example, the problem could be that the environment refers to a natural class or a phoneme that is not defined yet.
For more information, point to Resources on the Help menu, and then click Introduction to Parsing. See Allomorph Environments.