Just about everyone who wants to make a DVD has access to a computer and some kind of software to do it with. 

When you do it for the first time, it's all nerves and wondering if it will work. You compile your content and edit it into a work of art, even though it's Auntie Gertrude's rockin' nintieth birthday, make some jazzy menus with sounds and animation and you test it out on your computer. It works. It looks pretty cool. You're pleased with the fruits of your labour. You send out your lovingly hand made copies to all four relatives who were at the party and you get three calls back because your disc doesn't work. 

That's right. It fails. They put it into their DVD player hooked up to their gazillion inch nuclear powered plasma screen and all they see on the player's LED readout is "Searching" and then the player spits it out. And all the while you're thinking "What? I tested it and it worked!"

Bad news, sunshine. They're right that it doesn't work and here's why:

The majority of quality DVD players on the market today explicitly follow the standards laid out for manufacturers. To cover the part of the spec that is relevant to this topic, the player expects to find a certain file as the first file on the disc. The file name and the file position must match or the disc will be unplayable. Every other file involved must also be laid out in the correct order or the disc will not be playable. 

Your disc has all the files but not in the right place. 

The majority of quality CD and DVD burning software on the market work pretty well and will make DVDs that will play properly on the vast majority of players. However, they often have a feature where you can build a DVD file structure in a folder on your hard disk and then later burn it to the DVD-R. That's where it all comes unstuck. 

The problem is that even though the software creates the files, they won't be reassembled in the correct order at burn time. Chances are, it will just burn them in alphabetical order or some other arbitrary method. This is especially true for multi-format discs (i.e. contains a playable DVD and also software or other files not intended to used on a computer).

In general, unless you're confident that you're an expert, stick to using the 'wizard' or guided mode in your burning application. Save the project often as sometimes strange things can and will happen and you could lose all your hard work. And of course, make sure that when it comes time to burn the disc that there is nothing else running that could interrupt the flow of data to the DVD-R (i.e. no I/O overhead issues).

If you're trying to make a DVD with DVD-Video and DVD-ROM content, there are quite a few tricks and traps. We have a proprietary method of achieving an excellent result for our clients, so we can't talk about it here but we're willing to do it as part of a service and replication bundle. 

Hope this helps and happy burning!

Cheers - Virgil.