Accessing External List that uses BCS with CAML Query

Hi,

I have an external list that uses BCS to sql server. I can view the list with  Lists.asmx web service GetLlistItems. However, I get an parameter error when trying to add to the list with UpdateListItems. I will be changing over sharepoint lists to sql tables using BCS to connect to them and I need it to be seamless to clients that do CRUD operations using CAML. Are there any instructions on creating such an external list that maintains compatibility with ordinary sharepoint lists?