Hi,
The error message means that this control is declared more than one time.
When you use "Convert to Web Application", Visual Studio 2005 automatically generate a .designer.vb file for page. Please make sure that you don't declare it in another place. You can search it using Ctrl+Shift+F.
You also need to make sure that the designer file's Namespace matches codebehind Namespace.
I hope this helps.
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