Compilation tag throwing error in web.config

I have the following error in VS2010

Sections must only appear once per config file. See the help topic for exceptions.

It's pointing at the compilation tag, nested within the tag.

<system.web>
    <compilation>
          <assemblies>
            <add assembly="System.Data.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=..."/>
          </assemblies>
        </com开发者_Go百科pilation>
</system.web>

There are no other tags within the web.config.

My money is on a mal-formed comment or something - there has to be another compilation tag in there somewhere.

EDIT:

Try this - delete everything EXCEPT the compilation tag you showed us. Hit the site, which will probably fail, but not the same way. Add stuff back a little at a time until you get the dup-section error again