Double-clicking an Excel file does not open it

I received a call from a customer in distress today. They could not open Excel files by double-clicking on them. When they tried it, they received an error relating to Excel not being able to find the file. It said something along the lines of "Make sure you typed the name correctly..."

The customer is using Windows Vista with Microsoft Office 2007. I found a blog entry on the topic at http://www.vistax64.com/vista-general/45766-messages-make-sure-you-typed-name-correctly-4.html. For easy reference, I am posting it here as well:

"All pissing aside, here is the solution to clicking an excel file and
having Windows tell you the file is missing...
To resolve this problem, follow these steps:
1. In Microsoft Office Excel 2007, click the Microsoft Office Button,
and then click Excel Options.
2. Click Advanced, and then click to clear the Ignore other
applications check box in the General area.
3. Click OK.
1. In Microsoft Office Excel 2003 or earlier versions of Excel click
Options, on the Tools menu.
2. Click the General tab.
3. Click to clear the Ignore other applications check box, and then
click OK.
After you do this, you should be able to open workbooks by
double-clicking them in Windows Explorer."