>Here's my query:
>

>            var query = from m in _AdministrativeTabMappings.Elements("Mappings").Elements("Mapping")
>                        where m.Attribute("Page").Value == page
>                        select m;
>

>
>Query always returns a NullReferenceException. This works without the where clause. Page is a variable which I confirmed equals "bonds/administrator/AdministratorHome.aspx".

Page isn't an attribute, it's an element. An attribute would be something like:

<Page name="MyNameAttribute"Value</Page

I can't test this, but maybe something like this would work?

var query = from m in _AdministrativeTabMappings.Elements("Mappings").Decendants("Page")
                        where m.Value == page
                        select m;