Property 'DocEntry' of 'Document' is read only

Hi all

I've this error on My B1SO to B1SO scenario

com.sap.b1i.xcellerator.XcelleratorException: XCE001 Nested exception: com.sap.b1i.bizprocessor.BizProcException: BPE001 Nested exception: com.sap.b1i.xcellerator.XcelleratorException: XCE001 Nested exception: com.sap.b1i.xcellerator.XcelleratorException: XCE001 Nested exception: java.lang.RuntimeException: Invoke of: GetBusinessObjectFromXML Source: Description: CServiceData::VerifyPropertyWrite failed; Property 'DocEntry' of 'Document' is read only

BUI meta document is standard : BIUMETA.B1.8.8_B1.8.8.xml

I've created my custom ObjectType Z.B1.8.8_SO copied by B1.8.8_SO standard SAp Object :

so I've standard valuemapping Z.B1.2004_Doc (7 field)

and standard Key Policy 4 on keypath BOM/BO/Documents/row/DocEntry

I also tryed with keyplocy 2 but not run.

I don't know how to add query parameter

<QueryParams>

<DocEntry>

Value of the SO DocEntry

</DocEntry>

any idea ?