Dec 06, 2005 03:50 AM|Eilon|LINK
I think the issue might partially be a bug in the SqlDataSource control (someone else founds it not too long ago, if I recall).
I'm pretty sure that the workaround was to handle the "pre" event for the operation (e.g. Updating) and set the DbType manually:
e.Command.Parameters["myguidparam"].DbType = DbType.Guid;
And that solves the problem. It's unfortunate that the TypeCode enum (which is what Parameter uses for its Type property) doesn't have a Guid value.