Problem with Event Receiver

Hello,

I have a SharePoint Custom List and I’m going to update a database (none-SharePoint DB, located in different server) while my Custom List is changed (for example by adding new item).

I created a sandboxed solution and an event receiver for ItemAdding  and used linq for inserting new Item to a table called FromSharePoint:

 public override void ItemAdding(SPItemEventProperties properties)
       {
            String connectionString = “Data Source=172.16.0.15;Initial Catalog=test;Persist Security Info=True;User ID=sara;Password=123”;
           base.ItemAdding(properties);
           FromSharePoint fromSharePoint = new FromSharePoint();
           TestDataContext dc = new TestDataContext(connectionString);
           try
           {
               fromSharePoint.ItemID = Convert.ToInt32(properties.ListItem[“ID”]);
               fromSharePoint.Title = properties.ListItem[“Title”].ToString();
               dc.FromSharePoints.InsertOnSubmit(fromSharePoint);
               dc.SubmitChanges();
           }
           catch (Exception ex)
           {
               dc.ChangeConflicts.ResolveAll(System.Data.Linq.RefreshMode.OverwriteCurrentValues);
               dc.SubmitChanges();
           }
           finally
           {
               dc.Dispose();
           }
       }

However, by adding new item to the list I get the following error:

Request for the permission of type ‘System.Data.SqlClient.SqlClientPermission, System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089’ failed.

I tried following solutions but my problem is still remained:

• changing wss_mediumtrust.config and wss_minimaltrust.config like what mentioned in this post didn’t work
• Setting trust level  to Full in web.config didn’t work

I also tested my problem in a farm solution, interestingly I didn’t receive the above error but my database  didn’t change.

Does anyone have an idea??