You receive a "Cannot connect to the configuration database" error message when you connect to your Windows SharePoint Services Web site
http://support.microsoft.com/?id=823287
this fixes the issue
Method 3: Make Sure That the Account That Is Used By the Application Pool Is the Account That Has the Required Permissions to the SQL Server Database
'System.Data.MissingPrimaryKeyException' occurred in system.data.dll
To obtain additional information about the DataSet object, such as the primary key information, use one of the following methods: • Call the DataAdapter.FillSchema method to obtain extended schema information.
• Set DataAdapter.MissingSchemaAction to MissingSchemaAction.AddWithKey before you call the Fill method
Validation of viewstate MAC failed / The state information is invalid for this page and might be corrupted
viewStateEncryptionMode ="Never fixed the problem
Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true"
CodeFile="ReadData.aspx.cs" Inherits="ReadData" Title="Untitled Page"
EnableEventValidation="false"
viewStateEncryptionMode ="Never"
ADO.NET: DataTable already belongs to another DataSet.
workaround
DataView dv = new DataView(dsUsers.Tables[0]);
dv.RowFilter = "user_id = " + user_id;
dsUsers = new DataSet();
dsUsers.Tables.Add(dv.Table.Copy());
