Ghost Schemas and Incorrect Paths
If a file contains a reference to another file that cannot be found at the specified location—a so-called ghost file—, an error 
icon appears in the top left of its title bar. The ghost file is indicated by the ghost 
icon in its title bar. In the screenshot below, ipo.xsd has an Include statement that points to the schema address.xsd, which cannot be located at the location specified in the Include statement. In this case, address.xsd is the ghost schema file. Consequently, any file that references address.xsd is marked with the error icon, both in the Design window and in the Explorer window.
An XML instance is also marked and treated as ghost file if it cannot be found, for example:
A schema can be a ghost schema for any of several reasons. The most common are:
•The schema is not physically present at the specified location for any of several reasons. For example, it might have been moved.
•The schema cannot be loaded because the web server or network node is unavailable.
Note that ghost files are displayed in the Explorer and Design windows (even though they are not at the location specified in the reference). In the design, the connector line between the ghost file and its target schema is also displayed.
If you encounter incorrect references and ghost files, there are two possible ways to deal with the problem: