Login failure

I have posted many questions regarding this and don't seem to get it right. However, there is a twist to this. I think I succeeded in granting permission to the user 'quirverT', because when I tried to create a new account on my website, the error changed to this:

Server Error in '/' Application.
Login failed. The login is from an untrusted domain and cannot be used with Windows authentication.
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: Login failed. The login is from an untrusted domain and cannot be used with Windows authentication.

Source Error:

Line 41: cmd.Parameters.AddWithValue("@DeezNutz ", txtname.Text);
Line 42: cmd.Connection = con;
Line 43: con.Open();
Line 44: dr = cmd.ExecuteReader();
Line 45: }

Source File: g:\PleskVhosts\quirver.com\httpdocs\SignUp.aspx.cs Line: 43

Stack Trace:

[SqlException (0x80131904): Login failed. The login is from an untrusted domain and cannot be used with Windows authentication.]
System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling, SqlAuthenticationProviderManager sqlAuthProviderManager) +1524
System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions) +467
System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions) +70
System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) +940
System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) +111
System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection) +1567
System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection) +118 System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection) +268
System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource1 retry, DbConnectionOptions userOptions) +315 System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource1 retry) +128
System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +265
System.Data.SqlClient.SqlConnection.Open() +133
SignUp.Button1_Click(Object sender, EventArgs e) in g:\PleskVhosts\quirver.com\httpdocs\SignUp.aspx.cs:43
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +11596288
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +274
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1890