Error while reversing document in SAP using BAPI

Using BAPI_ACC_DOCUMENT_REV_POST to reverse entries posed via BAPI_ACC_DOCUMENT_POST, however we are getting following errors

E RW 609 Error in document: BKPFF $ SYS600 BKPFF

E RW 632 Document BKPFF 900026 SYS600 cannot be reversed BKPFF

E RW 630 Reversal in component Financial Accounting not possible Financial Accounting

E F5A 9 Reversal not possible, accounting document for the ref. does not exist BKPFF

code for reference

Dim companyAPI As IRfcFunction = _ecc.Repository.CreateFunction("BAPI_ACC_DOCUMENT_REV_POST")
    Dim rev As IRfcStructure = companyAPI.GetStructure("REVERSAL")
    rev.SetValue("OBJ_TYPE", "BKPFF")
    rev.SetValue("OBJ_SYS", "$")
    rev.SetValue("OBJ_KEY", "900026N0342016")
    rev.SetValue("OBJ_KEY_R", "900026N0342016")
    rev.SetValue("COMP_CODE", "D756")
    rev.SetValue("REASON_REV", "01")
    Dim transfunction = _ecc.Repository.CreateFunction("BAPI_TRANSACTION_COMMIT")
    transfunction.SetValue("WAIT", "X")
    companyAPI.Invoke(_ecc) 
    transfunction.Invoke(_ecc)
    Dim dt As DataTable = GetDataTableFromRFCTable(companyAPI.GetTable("RETURN"))