This file does not have a program associated with it - what does this mean and what do I do?

In email, this most commonly happens when someone sends you an attachment with data created by a program you don't have. For example if someone were to send me a ".psd" file, when I attempt to open it, I might get this error:

The reason? I apparently don't have a program installed that understands what to do with a ".psd" file. As a result, I cannot open the file.

The most common way to resolve this issue is simply to install a program that understands files of that type. In most cases, when a program is installed, it also sets up the associations for all the file types that it understands. In this case, if I were to install Adobe PhotoShop, which understands ".psd" files, then I should be able to open them without a problem. Attempting to open a ".psd" file would then start up PhotoShop, which in turn would read and display the file.

Sometimes these associations between file extensions and the programs that understand them can get lost, or confused. The second most common way to resolve this is to use the application that should understand to repair the associations. If you know, for example, that you have a program that understands the file, but you're still getting that error, there are some common approaches:

• Many applications allow you to control exactly what file extensions they are supposed to support in their options. Fire up the application that's supposed to handle that file type, and search for its options dialog, or other settings. If you find the ability to associate the program with a particular file extension, this can resolve the problem.

• As I mentioned, many programs set up their associations when installed. If the program offers it, in Control Panel, Add/Remove programs, find the program that's supposed to handle this file type, and perform a "repair" install.

• If "repair" doesn't work, or isn't available, then a full uninstall and re-install of the application may do it.

A good example of a "repair" that's not at all obvious, is the solution for Windows Picture and Fax Viewer. If you want to restore the association between Windows Picture and Fax Viewer and most image files - meaning you want to view most image files using Windows Picture and Fax Viewer - then click Start, Run and type in the following cryptic command:

regsvr32 /i shimgvw.dll

Press OK a couple of times and things are reset. This doesn't work for everything, but it's an example of how many programs have the ability to reset their associations without needing to be reinstalled.

OK, what if none of that works, or for some reason you want to do things the hard way ... er, by hand?

First, you need to know what program you want to use to open a particular file, and that program must already be installed on your machine.

Now, fire up Windows Explorer (right click on My Computer and click on Explore is one quick way). Click on the Tools menu and then the Folder Options item. In the resulting dialog, click on the File Types tab, and you should see something like this:

In that list, scroll down to the file type, the "extension" you want to add or modify. I'll continue with my example and look for "psd". It's not on the list, so I'll click on New, where I'm presented with this dialog:

Note that I've already typed in "psd".

Now, all that did is create an empty entry in the list:

Once it's in the list - or if it already was - we click on Change and ... oops, we get this message:

Since we're doing this manually, we'll "Select the program from a list", and click OK. We're then presented with a list of the installed software on your machine:

•

In my case I happen to know that a program I have installed, Firehand Ember, will also read my "psd" files, so I click on that, make sure that "Always use the selected program to open this kind of file" is checked, and press OK. Now when I try to open a ".psd" file, Firehand Ember will be launched and used to display the file.

Obviously you'll need to choose both the correct extension and program for the problem you're attempting to solve.

Quite often you'll be faced with a file extension and have no clue as to what it is, or what program should be used to open it. There's often no single answer, but a good resource to research the meaning of various file extensions is FileExt.com. There you can enter an extension and it will list all the possible meanings, including the most likely or most common use.

Why do I say there's often no single answers? Because there's nothing to prevent two or more different and totally unrelated programs from using the same file extension for totally different things. A great example is the ".dat" file - I count well over 20 different possibilities, and there are probably many, many more. In case like this, you'll need to know more about what program was used to create the file before you can make a choice on how to open it.