VB与数据库连接不能放在模块中，请大家帮下忙，谢谢

rivate Sub cmdOK_Click()
'注册新用户

Dim cnn1 As ADODB.Connection
Dim AddUser As New ADODB.Recordset
Dim SqlStr As String
Dim DBstr As String
Dim UsrName As String
Dim UsrPwd As String
Dim strCnn As String

'与数据库连接
Set cnn1 = New ADODB.Connection
strCnn = "Provider = SQLOLEDB; Data Source = localhost ;User ID = sa; & _
Initial catalog = wastebook ;Password = ;"
cnn1.Open strCnn

'与表连接
Set AddUser = New ADODB.Recordset
AddUser.CursorType = adOpenKeyset
AddUser.LockType = adLockOptimistic
×× AddUser.Open "UserInfo", cnn1, adOpenForwardOnly, adLockOptimistic
End Sub
以上代码通过，于是我新建了一个模块，并Public g_Conn As ADODB.Connection 把g_Conn设为全局变量，在模块中
'建立连接
Set g_Conn = New ADODB.Connection
strCnn = "Provider = SQLOLEDB; Data Source = ServerName ;User ID = UserName;" & _
"Initial catalog = DBName ;Password = UserPwd; "
g_Conn.Open strCnn
而把上面与数据库的连接代码去掉，运行就会报错“连接无法用于执行此操作。在此上下文中它可能已经被关闭或无效。错误的是带××的那行，请大家帮忙，谢谢：）