What do I do when a program reports a DLL is missing?

It depends on the program.

In this case ideally we’d get a little more information, but lets see how
far we can get and come up with some general troubleshooting rules along the
way.

“It cannot load the DLL” could mean several things and unfortunately we
don’t know what the exact error message was. If it couldn’t find it, it’s
possible that the DLL is simply in the wrong place since the person asking
pointed out that it was on the disk. If it had a problem loading it,
then perhaps it’s corrupt or perhaps it’s in use by some other
application.

For a missing, misplaced, or corrupt DLL, reinstalling or repairing the
application is often the right course of action. It’s possible that this is a
Windows XP DLL, in which case a System File
Check might repair the problem. If it’s a Outlook Express DLL, then
reinstalling Outlook Express (typically with the latest
version) could be the right way to proceed.

If the DLL is in use by another program it’s possible that program has
locked access to it for some reason. The techniques in the previous article How can I find out who is using a “file in
use”? can be used to determine who’s using a DLL. Perhaps shutting down
that program, if possible, will allow you to start Outlook Express.

And of course, it’s quite possible that it’s none of the above. Error
messages typically contain important information to help track down these types
of things, so we’d probably need to see the specifics to make a further
determination.