Thank you for writing.
Let me get straight to the issues at hand:
1. Please substitute the RadToolStripSeparatorItem
2. & 3. In version Q2 2011 the namespaces ComboBox
do not comprise any classes. In this sense, if your project really uses Q2 2011, you should be able to remove the references without causing any errors.
If you encounter difficulties during the upgrade process, feel free to contact me back.
the Telerik team