不知道如何改错，大家帮小弟我看下

不知道怎么改错，大家帮我看下
Server   Error   in   '/Oi '   Application.
--------------------------------------------

Compilation   Error  
Description:   An   error   occurred   during   the   compilation   of   a   resource   required   to   service   this   request.   Please   review   the   following   specific   error   details   and   modify   your   source   code   appropriately.  

Compiler   Error   Message:   CS0104:   'TreeNode '   is   an   ambiguous   reference   between   'System.Web.UI.WebControls.TreeNode '   and   'Microsoft.Web.UI.WebControls.TreeNode '

Source   Error:

 

Line   71:  
Line   72:   }
Line   73:   private   void   CreateDataSource   (string   Parentid,   ref   TreeNode   Pnode)
Line   74:   {
Line   75:   string   sqlstr   = "       select   distinct   m.id,   m.ModuleID,m.modulename,m.menupath,m.parentmoduleid   ";
 

Source   File:   c:\Inetpub\wwwroot\OI\Manage\Tree.aspx.cs         Line:   73

[解决办法]
ref 传的参数需要给变量赋值，你应该没有给变量赋值。
如
int i = 1;
int add(ref i)
{
}