Why can't I open this file?

Files can appear read-only for one several reasons, the most common being:

• The file is marked read-only. Individual files can be marked as being read-only - typically as a means to protect them from being overwritten.

• The file is on a media that is read-only. CD-R's are write-once media. Once a CD-R has been burned, it cannot be written to - it can only be read. Hence the files on it are marked as "read-only".

• The file is in use. Less frequently, another program might have the file open in such a way that anyone can read it, but the file is locked for writing. In some cases this can be reported as the file being "read-only".

Let's look at what we can do about each of those.

If a file is marked as read-only on the disk, it's fairly easy to reset that attribute.

Fire up Windows Explorer, and locate the file in question. Here I've located "c:\documents and settings\leon\my documents\safeontheinternet.pdf":

Now, right click on the file you want to change, and click on Properties. You should see a dialog much like this one:

Note the Attribute setting "Read Only" - uncheck it if it's checked, and press OK. If no error appears, the setting has been removed.

If the file is on a read-only media like a CD-R or a read-only network share, you cannot change the read-only status. In this situation, or if you just want to avoid changing the read-only status of the file as we just did, the next best solution is to make a copy of the file onto your local hard disk.

So, using Windows Explorer, the command prompt, or whatever means you use to copy files, copy the file or files from the read-only media to a folder on your hard disk.

Important! When you copy a file from a read-only media such as a CD-R, the read-only status is copied with it. That means you still can't write to the file until you take the steps above to reset the read-only attribute on the file on your hard disk.

This causes people no end of confusion.

Finally, if the file is in use, you again, can either make a copy of it, or determine who's using the file and close that program.

While the question asks specifically about Excel, in fact the most common scenario where this whole read-only problem comes up is when email folders are copied to CD-R for backup or for moving to a different machine.

Mail programs, particularly Outlook and Outlook Express, expect - and require - that they be able to write to the files containing email. If these files are marked read-only then the program will either fail to open them, or worse, tell you that they don't exist.

And remember - copying the files to your local hard disk isn't enough. I see people frequently stymied because they've copied their files locally thinking that was enough, and they still can't open their mail.

After copying files from CD-R you still must reset the read-only attribute if you want to be able to write to them.

And naturally that holds true for the Excel file we started with. Copy the file to your hard disk, reset the read-only attribute, and you should be good to go.