Question : Asp.Net Conversion failed when converting from a character string to uniqueidentifier.

this is my string:
            SelectCommand="SELECT '' as UserId, '' as [Company], '' as [WebSiteUrl] UNION SELECT UserId, Company, WebSiteUrl FROM [UserProfile] ORDER BY [Company]">

this is my error:
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Conversion failed when converting from a character string to uniqueidentifier.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Data.SqlClient.SqlException: Conversion failed when converting from a character string to uniqueidentifier.
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this portion of my code:  can be: '' as UserId or '0' as UserId that for a string or a int
I do not know what it would take to convert the Guid to a string as to replace '' as UserId.

Answer : Asp.Net Conversion failed when converting from a character string to uniqueidentifier.

how about this one:
SelectCommand="SELECT '"+Guid.Empty.ToString()+"' as UserId, '' as  [Company], '' as [WebSiteUrl] UNION SELECT UserId, Company, WebSiteUrl  FROM [UserProfile] ORDER BY [Company]"