Inserting values into custom class error

I use MSCS2002 + SP3 + FP1

     I have extended dw with a custom class Region_ZipCode (consisting 
of 2 fields) with the use of 'CreateSchemaObject.vbs' script from SDK:

CreateClassDef cn, "Region_ZipCode", "test_Source", "", True, 0, ""
CreateMemberDef cn, "Region_ZipCode", "Zip", "WSTR8",
   fGenerateColDef + fIsRequired + fPrimaryKey + fHasDefaultVal, "0", ""
CreateMemberDef cn, "Region_ZipCode", "Region_ID", "NUMBER",
   fGenerateColDef + fIsRequired, "", ""

     After that I try to execute the following code (written in c#):

ADODB.Connection adoConnection = new ADODB.ConnectionClass();
adoConnection.Open("Provider=commerce.dso.1;Data 
Source=mscop://InProcConnect/Server=my_server: 
Catalog=DWSchema:Database=my_database:FastLoad=True:Connection_Retry=10:Connection_Retry_Delay=30",

"my_user", "my_password", 0);
object nullObject = Type.Missing;
adoConnection.Execute("DELETE FROM Metro_ZipCode", out nullObject, 0);
adoConnection.Execute("INSERT INTO Region_ZipCode (Region_ID, Zip) 
VALUES (1, '99999')", out nullObject, 0);
adoConnection.Close();


     The first "Execute" command is successful.
     The second one throws the following exception: "Exception from 
HRESULT: 0xCA2D8038." And no more information.

     Please, advice.

-- 
Yours faithfully,
Alexander Yushchenko