I should include that I tried playing the exact same file on both the 1 and 8 GB flash drives, as well as on a DVD. The same file will play on all except the new 8GB drive.
I can't find anything anywhere that addresses what might be only my problem apparently. I bought an 8GB flash drive (Intenso) that I have returned for a different brand, now CnMemory, also 8GB. Neither will play on my Mustek MP70B DVD player. However I do have a 1GB MP3 player that will play an .avi movie (or music, jpg, etc.), but neither of the others will play anything. In fact when it tries to read it, it powers off, comes back on, and powers off continually in a cycle.
I have not found anywhere that portable DVD players can't handle 8GB flash drives. The drives are formatted to FAT32, not NTFS, which I know they can't read. If there is any sort of compatibility issue, I can't find it. All are 2.0, FAT32, and the only difference is 8 instead of 1 GB.