Windows Installer: Registry path + Fixed path

[MW]

Hi all,

I have writen plugin for another application and I need to install this
component in a directory where the application is installed.
I am using the basic Windows Installer.
I read the value from a registry to get the proper directory. The problem is
that I need it to input in that way in the given directory:

APPLICATION_PATH \ ANOTHER_DIR

So I created Custom Folder in an installer. I've set the Default Location
property to the: [RegistryPath][Another_Dir]
So this should work perfect. Unfortunately there is a property named
Property, that can override the Default Location.
In MSDN I found that if I left it empty, then it will never override it
(that's the way I want it) , but when I leave it empty, the compiler states:

Invalid property " for folder 'AnotherDir'

How do I get rid of this error?
Is there any other solution, maybe?
If something is unclear let me know.

Thanks for all the help.