Data reader probelm with my sql

Thanks for your reply dear,
I am passing the string (a Name) through a text box and first time it works fine. When the input is given through the same text box second time onwards the datareader returns null (even for the same Name). The text box input, the stored variable string, syntax everything I hvae checked and everthing is OK. The data reader is not getting refreshed for a second query..please...

Here is a brief account of the problem

Sql_data_connec tion is the dataconnection to my mysql database
QueryString is sql statement as given below

All the above information I am passing to the code check_user as given below
...