Server Error in '/ADO.Net' Application.
The variable name '@param' has already been declared. Variable names must be unique within a query batch or stored procedure.
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: The variable name '@param' has already been declared. Variable names must be unique within a query batch or stored procedure.
Cause
This error occurs when SQL server finds two variables or parameters of same name and hence the ADO.Net class throws the above exception.
Solution
1. If you are running a loop and using the same command object to insert data add this statement
2. Check if you have not passed the same parameter twice like
cmd.Parameters.AddWithValue("@city", txtCity.Text.Trim());
cmd.Parameters.AddWithValue("@city", txtCity.Text.Trim());
3. If using stored procedure check if you have duplicate variables if you found remove them.
For example
DECLARE @CustID varchar(10)
SET @CustID= 'ALFKI'
SELECT *FROM Customers WHERE CustomerID = @CustID
DECLARE @CustID varchar(50)
The above query will give the same error.
If anyone else some other solutions that helped them, please share.