The error is referring to a Class structure identity. Looking at the representation, BPC is reference to the class BPC (BPCUSTOMER), on that class there is a collection called BPD (Customer delivery address) which is class BPDLVCUST. On the class BPDLVCUST is a another collection called C_REP (Customer reps) which is linked to the sales representative. My assumption is that the class SALESREP which this datatype is associated with is corrupted. Try validating the class SALESREP, or do a System Class validation and Link resync. 

The error is referring to a Class structure identity. Looking at the representation, BPC is reference to the class BPC (BPCUSTOMER), on that class there is a collection called BPD (Customer delivery address) which is class BPDLVCUST. On the class BPDLVCUST is a another collection called C_REP (Customer reps) which is linked to the sales representative. My assumption is that the class SALESREP which this datatype is associated with is corrupted. Try validating the class SALESREP, or do a System Class validation and Link resync. 

thank you for your response it makes it more clear,but i just did System Class validation then a link resync for all tables but the error persist

If I understand correctly, you are trying to modify the customer record? Currently the $create facet is not active on this Class. Only the $details (equates to read) and $edit (modification) facets are currently working.

oh ! i didn't know about that, and how to know which available facets on every table ? or just detailsand edit for every table ? 

You can have a look in the Class and Representation, there is a description attached in the help file.

https://online-help.sageerpx3.com/erp/12/staticpost/representation-management/?highlight=%24edit

Very few currently allow for creation, there are some but its on a case by case situation. Best for now is to make use of the SOAP AOWSIMPORT / AOWSEXPORT if you want to create entries,

sorry i didn't find the description attached in the help file for which available facets on every table . but i think i am limited with REST API, so i will take a look about old SOAP web service. thank you so much for your help.