TreeView states that it is unable to find CSS style, XML file or images. The ASPX page is in subfolder.
You should use the tilde ("~") symbol. It is an abbreviation for the home directory of web application. Tilde can be used in property values, XML Structure, CSS Style, templates, etc.
This feature is very useful because User Control with a TreeView can be placed on the ASPX pages, which are located in different subdirectories of the web application.
Examples of using:
<item title="Subfolder Page" href = "~/Subfolder/Default.aspx" />
The CSS style can include the tilde ("~") symbol only if the TreeView component loads the CSS style from a Skin Folder as specified by the CSSSource property.