The most common reason this occurs is that the sys_id stored in the record does not point to a valid record. In your case, the stored value is "Holcim Services EMEA", which most likely is not a valid sys_id. This can occur for example if a script sets the value and puts in the incorrect field.
Another common scenario is that the target record was deleted and the record containing the reference was manually imported after the deletion, for example via XML files.
Either way, you'll have to fix the references.
