How to delete users when using the membership class?

Hello,
I currently built a custom form using VS 2005 to accommodate administrators when deleting users from the  membership "aspnetdb" database.
I set the method for the objectDataSource to use "DeleteUser(String username, Boolean delete All Related Data), returns Boolean".
When I run the application and click the delete link from my gridview I receive the following error message:
"Value cannot be null. Parameter name: username"
Of course this is cause by the string username not receiving any data which leaves it null, so how do I supply the parameter username with the right data?
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