[Shotwell] video files remain in 'missing files'

[Bart Vandewoestyne <Bart Vandewoestyne telenet be>]

Hello list,

I have 125 video files that I cannot get away from my 'Missing Files', 
although I know the video files exist on my external harddrive in the 
Pictures folder.

The photo disk is mounted as follows:

/dev/sdc1 on /media/bart/FOTO_DISK type vfat 
(rw,nosuid,nodev,relatime,uid=1000,gid=1000,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,showexec,utf8,flush,errors=remount-ro,uhelper=udisks2)

One of the reported 'Missing Files' is for example MVI_8537.MOV. 
However, that video file *does* exist under the Pictures directory:

bart kulak:/media/bart/FOTO_DISK$ find Pictures/ -name MVI_8537.MOV
Pictures/2011/10/30/MVI_8537.MOV

Shotwell was able to re-locate/find all my photos in .jpg format, but it 
seems like it cannot re-locate/find some .MOV, .MP4, .AVI and .3gp video 
files.

For as far as I can check in Edit->Preferences->Library Location, the 
directory where to import fotos to is set to the correct Pictures directory.

What can I do to make Shotwell find these files again?

Kind regards,
Bart