DI API Problem in Patch 30-SAP 2007 A

Hi,

I have created one UDF in the marketing documents(Type combo box and i set the default value to "-","-") and i am try to assign the new value to the UDF through DI API . I am getting the following error,

" 3 is not a valid values for property "U_BPProj". The valid values are "-","-"

Here 3 is my value.

my Coding

oSalesQuotation.Lines.UserFields.Fields.Item("U_BPProj").Value = strBPProject

oSalesQuotation.update

I am using 2007A patch Level 30.

Thanks and regards

Senthil.