System.AccessViolationException”类型的未经处理的异常在 System.Data.dll 中发生。其它信息：尝试读取或写入受保护的内存。这通常指示其它内存已损坏。

错误背景：

操作系统：编程环境：VS2013。语言：VB.net；数据库：SQLserver2008

做数据库连接时。发生的错误：

错误提示为：

说明：用VB.net连接SQLServer数据库

第一种情况：

连接字符串为“Server=(Local);Database=charge_sys;UserID = sa;Password=123456”时，连接没问题；

另外一种情况：

当把“ Server=(Local)”换为 “ Server=192.168.24.123 ”。即把local换为数据库serverIP地址时，连接不成功。出现如上错误（PS：其它人的机器上就能够）。

第一种情况的代码：

    Public Class UserDAO
        Public connStr As String = "Server=(Local);Database=charge_sys;User ID = sa;Password=123456"
        Public Function UserLogin(ByVal userName As String, ByVal password As String) As Boolean
     <span style="white-space:pre">	</span>    Dim conn As New SqlConnection(connStr)
            Dim dbcmd As New SqlCommand
            Dim reader As SqlDataReader
       <span style="white-space:pre">	</span>    Dim sqlStr As String = "select * from User_Info where userID=@userName and PWD=@password"
            '与数据库建立连接
            conn.Open()
            '操作数据库
            dbcmd = New SqlCommand(sqlStr, conn)
            dbcmd.Parameters.Add(New SqlParameter("@userName", userName))
            dbcmd.Parameters.Add(New SqlParameter("@password", password))
            reader = dbcmd.ExecuteReader
            If reader.Read Then
                Return True
            Else
                Return False
            End If
            '关闭与数据库的连接
            conn.Close()
        End Function
    End Class

另外一种情况的代码

    Public Class UserDAO
        Public connStr As String = "Server=192.168.24.123;Database=charge_sys;User ID = sa;Password=123456"
        Public Function UserLogin(ByVal userName As String, ByVal password As String) As Boolean
     <span>	</span>    Dim conn As New SqlConnection(connStr)
            Dim dbcmd As New SqlCommand
            Dim reader As SqlDataReader
       <span>	</span>    Dim sqlStr As String = "select * from User_Info where userID=@userName and PWD=@password"
            '与数据库建立连接
            conn.Open()
            '操作数据库
            dbcmd = New SqlCommand(sqlStr, conn)
            dbcmd.Parameters.Add(New SqlParameter("@userName", userName))
            dbcmd.Parameters.Add(New SqlParameter("@password", password))
            reader = dbcmd.ExecuteReader
            If reader.Read Then
                Return True
            Else
                Return False
            End If
            '关闭与数据库的连接
            conn.Close()
        End Function
    End Class

两种代码的不同之处只在于数据库连接字符串中的Server值不同。