The virtual path 'x' maps to another application, which is not allowed.

Hi,
I have several sub web applications and a 'core' web application which form a complete web application.  One of these sub web applications is my UI handler consisting of master pages.  However not only the parent application needs to reference the sub web application (because it is located below this is ok), but also the sub web applications.  My ASPX pages on pre_init() loads the master page by using the path '..\CoreUI\MasterPages\MasterPage.master' rather than using '~' because this will resolve to the root of the current sub web-application.  I use '..\' to reference the sub UI application that is above and at the same level of the application.
However, I get the error above.  I understand IIS doesn't want me to use pages above in another application, but how can I get round this?


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