Problem with DVDs caused by slow USB?

[Ridicully]

I have been producing some DVDs that have strange problems and I only have a faint idea of what is causing them. Basically when I put my DVD into different DVD players, it may or may not play, or may play albeit with some problems.

The description of various outcomes for each scenario:

1. Play with PowerDVD 4 on computer: the film plays for about 2 seconds and closes.
2. Play with PowerDVD 5 or PowerDVD DX on computer: No problems whatsoever
3. Play with Video Player: Works perfectly
4. Play with another video player: plays but some subtitles missing (?!)
5. Play with another video player: does not play
(Unfortunately I cannot remember the models of the video players... they all belong to my University's library...)

I tried another DVD with the same files on it that I burnt with another computer, and it worked OK on all 5! So I suspect the problem is with the laptop or the DVD-R burner I am using now! I have a very old laptop that still has USB 1.1 even though it is WinXP, and my DVD-writer (NEC 3550A) is connected externally by USB.

The DVD is made by burning Video_TS and Audio_TS folders onto DVD-R using Nero Burning Rom in Nero OEM (version 6.6.1.4). The speed used is 2x.

So I am wondering if anyone knows whether a slow USB speed may cause the DVD burnt with external writer to be not playable by some video players/applications or lose subtitles? I really hope someone can confirm this before I plonk $30 into buying a USB 2.0 card for my laptop!!!