How do I deal with this error when calling an API to update an instance? The Object Version Number

I'm calling csi_item_instance_pub.update_item_instance to update extended attributes, and am getting this error message from the API:

The Object Version Number passed does not match with the one existing in Installed Base tables1

I've checked the answer from another, related thread about checking a concurrent manager setting, and it was already set to the correct value. 

I guess I don't understand what data I'm supposed to assign into the object_version_number fields in the records you pass into the API.  Can anyone shed some light on this?  I'm trying to update the values of 6 different extended attributes, and the Metalink note about populating these records simply shows them assiging the value of '4' into the object_verson_number fields.  I  need to know what value I should assign into those fields.