SAP Note 16734 - Classes: Restrictions to Characteristic Names

Symptom:

As of release 2.2, you can no longer use special characters in characteristic names in the classification system. This is to ensure compatibility with the variant configuration system.

Cause and prerequisites

Enhancements to the R/3 System.

Solution
Provided that the variant configuration system is not being used, the characteristic names which have already been assigned can still be used without any restrictions. However, you cannot create new characteristics with special characters in their names.
In Customizing for characteristics, you can define that existing characteristics which do not comply with the naming conventions can be renamed.