<p>I am a developer for a .net application that uses ClickOnce for deployment. I have deployed it over 60 times and computers have not had any issues downloading the latest release. However, when I deployed this morning, the following error occurs when computers with Office 2007 installed tries to start the application:</p>

<blockquote>
  <p>Unable to install or run the application. The application requires that assembly stdole Version 7.0.3300.0 be installed in the Global Assembly Cache (GAC) first. Please contact your system administrator.</p>
</blockquote>

<p>However, computers with Office 2003 can start the application with no problem.</p>

<p>Does anyone have any recommendations on resolving this issue?</p>

I am not sure about your particular problem, but the Office 12 version of the stdole library is different (and -in my experience- not always backwards compatible) than then one you have when you use Office 2003.
We use a wrapper around the Office DLLs to use the Mailmerge features Office has to offer and, believe it or not, Microsoft changed the interfaces
again
, therefore we have to compile
two
different wrappers, linked against
two
different office versions. In short, a PITA.
I am not coding against MS office again until they don't provide a Managed library.
Despite the rant, I think that you should install Office 12 in your computer and test from there. You'll notice that all the Office stuff is different. If you can make it work under Office 12 it
may
be compatible with machines with Office 11 (also known as 2003), but don't count on it and test it before deploying anything.
I don't think that this has anything to do with ClickOnce; it's more a GAC/OfficeVersion issue. Also, check for possible Vista problems, as the UAC and the DEP stuff tend to interfere with the way "old" applications used to work.