I'm pretty sure that it's a length problem rather than a file corruption problem, because (a) it happens with the two shortest files in the collection, and only with those two (both of which are 1.5M, and a second or so in length), (b) PD8 had no trouble importing them, and (c) they play just fine in Windows media player.
I'm not sure how useful these very short clips will be, but it would be nice to have them in the library nevertheless. Can anyone suggest anything that might help?