Custom Web Errors used by WebSites and Virtual Directories. You can only use error code and sub code combinations which are supported by IIS. Attempting to set a custom error for an error code and sub code combination that is not supported by IIS (in the default list of error codes) will result in an installation failure. Extensibility point in the WiX XML Schema. Schema extensions can register additional elements at this point in the schema. HTTP 1.1 error code. Error sub code. Set to 0 to get the wild card "*". File to be sent to the client for this error code and sub code. This can be formatted. For example: [#FileId]. URL to be sent to the client for this error code and sub code. This can be formatted. Extensibility point in the WiX XML Schema. Schema extensions can register additional attributes at this point in the schema.