How to get sharepoint to update guid field in an external list

Hi all,

I have a SQL table which I wish to use SharePoint Foundation 2013 to update. The idea is to use sharepoint as a web interface to update, delete and create table items in a SQL database.

I am using a guid as a primary key in the table.

I am using an external list to connect to and display the information from this table in sharepoint.

I can delete and update table items successfully.

I can create a table item, however I can only do this one.

I worked out that the guid in the table for the new item I am creating is all zeros in guid format in the SQL table.

This means that I can only create one item, the next time I try I get this error:

Failed to create a list item for this external list based on the Entity (External Content Type)

This is because the next item I create in the table also has a guid of all zeros so it would be a duplicate.

Is there a way that I can have sharepoint create a new guid so that this doesn't happen?

thanks

Jason