The root cause of this message is most likely that the enumeration is first defined programmatically (e.g. 'Simulink.defineIntEnumType') and Simulink then attempts to redefine it when loading a model linked to a data dictionary which contains a second enumeration definition.
In order to prevent these issues, you may wish to employ the following commands:
This will clear enum definitions created by the "Simulink.defineIntEnumType" command.
This will close connections to data dictionaries that are presently open. If a data dictionary contains an enum definition, closing the dictionary will attempt to release this enum definition from memory.
For additional information related to these functions please reference the following documentation pages: