The field name is not valid.
When enabling some geodatabase functionality, there may be column names that have been reserved. For example, when creating an intermediate table in a new relationship class, the RID field name is used as the relationship ID field and cannot be duplicated. Another example is when a geometric network is created, fields are added to the participating feature classes to manage network behavior. One of these field names is already in use and is not valid.
Choose another field name.