Linking gridview and detailsview with Guids

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I have a gridview where the datasource is a list of products, and the
product id is a guid. The details view is the a list of the product
details. If all the select commands are internal to the application, it
runs fine, but if I put the select commands ina stored procedure, I get
errors: If I make the details view datasources control parameter an object,
I get this error: System.Data.SqlClient.SqlException: Implicit conversion
from data type sql_variant to varchar is not allowed. Use the CONVERT
function to run this query.

If I make the details view datasources control parameter a string, I get
this error:
Object must implement IConvertible.

How do I fix this? I've even tried using convert in the stored procedure
"Convert(varchar(50), ID)"