主题：[求助]关于窗口中嵌套独立窗口或者模式窗口的问题

请教老师，新建的项目测试下列代码

Dim tab As WinForm.TabControl = e.form.Controls("TabControl1")
Dim Name As String = "窗口B"

tab.TabPages.Add(e.sender.name,e.sender.name)
Dim pb = tab.BaseControl
Forms(Name).OPEN(-1000,-1500)

Forms(Name).BaseForm.TopLevel = False    ‘到这行报错：未将对象引用设置到对象的实例。

Forms(Name).BaseForm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
Forms(Name).BaseForm.Dock = System.Windows.Forms.DockStyle.Fill
PB.TabPages(e.sender.name).Controls.Clear
PB.TabPages(e.sender.name).Controls.add(Forms(Name).BaseForm)
tab.SelectedPage = tab.TabPages(e.sender.name)

有可能是什么问题？