this generally means that there's an incident which has an enumeration which has this value. This is likely produced by importing a management pack which defines this enumeration and then later remove the enumeration or management pack. The data in the CMDB is not changed, even though that enumeration value is gone. It's not an error, because it's valid data, but I can't look up the strings associated with the enumeration any longer (it's really not something that you need to resolve, unless it bugs you too much)
jim