>>>Never mind
>>
>>I assume this is associated with the 'Specifying location of SiteMaster' post. :-}
>>
>>IAC, if you want to keep the SiteMaster page identical in both sites I was going to suggest using 'Add Existing Item' using the 'Add as Link' option.
>>That will ensure that any changes are reflected in both sites.
>
>I replied to your message a few minutes ago but all what I typed (the entire paragraph) is gone now. Strange.
>
>Anyway,
>You are correct that my issue has to do with the Site.Master. Here is the latest thing that I am trying to resolve:
>1. Changed the location of the MasterPageFile in the child project (running in the virtual application) from ~/Site.Master to /Site.Master (since tilde refers to the root of the site).
>2. The parent site (running in the root folder) does not have Site.Master. And the parent site runs under Forms Authentication
>3. I changed the web.config of the child site to run under Anonymous Authentication.
>
>So now when I try to open a page from the child application (e.g. MyChildPage.aspx) as follows:
>

>mycomputername/MyMainApp/MyChildApp/MyChildPage.aspx
>

>
>I get error:
>

>The virtual path '/Site.Master' maps to another application, which is not allowed.
>

>Source error points to this:
>

>@ Page Title="User Login" Language="C#" MasterPageFile="/Site.Master"
>

>
>Please let me know if you see what I am missing. Thank you.
>
>UPDATE. I found the problem (can't explain it though). When I changed the location of MasterPageFile from
>

>MasterPageFile="/Site.Master"
>

>to
>

>MasterPageFile="./Site.Master"
>(just added a period before the first slash)
>

>
>I no longer get error. On to the next test.

Glad you got it working (but I'm not sure why that made a difference either).

Looking at this it seems as if a good solution is to:
(a) put your sitemaster files in a folder outside the IIS structure.
(b) Create a virtual directory (for e.g. named 'Masters') in the root of your website pointing to the physical folder above.
(c) Change the aspx page MasterPageFile attribute to '~/Masters/Site.Master"

That allows you to use the same Site.Master in multiple sites.
Note : Depending on the project type you may, in Site.Master, need to change the CodeBehind Attribute to CodeFile