Well discussed limitation.
by R. Proffitt - 4/21/11 4:51 PM
In Reply to: Inconsistent creation of thumbnails on video files in WinXP by jbouvard
Windows only knew a few video encodings back then. Later folk created CODECs to add more but as you have discovered these can fail on some files. There are no plans to fix this as most CODECs are not from MSFT and XP's fixit team is long retired.
You may want to change the icon of the file manually or research titles like CODEC SNIPER and look for fixed codecs.
There are other reasons for this and it's a cache limit or a corrupt cache. Here's two googles about each.