can't grab the same dvd anymore: any help?

Hi all!

I have this DVD recorded in a stand alone player and i could grab it
previously, but i tried again today and it didnt work. Here's the log:

[truncated 50 lines]
Fri May 18 15:49:56 2007 Start job 'Process preview frame - title #1'
Fri May 18 15:49:56 2007 Start job 'Grab preview - title #1'
Fri May 18 15:49:56 2007 Executing command: mkdir -m 0775
/tmp/dvdrip10167.ppm; cd /tmp/dvdrip10167.ppm; execflow transcode  -H 10
--print_status 25 -o snapshot -y ppm,null -x vob,null -i
/home/timmy/dvdrip-data/jool-holland/vob/001/ -S 140 -c 1-2 -L 1323715 &&
execflow convert -size 352x480 /tmp/dvdrip10167.ppm/snapshot*.ppm
/home/timmy/dvdrip-data/jool-holland/tmp/jool-holland-001-preview-orig.jpg&&
execflow convert -size 352x480 /tmp/dvdrip10167.ppm/snapshot*.ppm
gray:/home/timmy/dvdrip-data/jool-holland/tmp/jool-
holland-001-preview-orig.raw && rm -r /tmp/dvdrip10167.ppm && echo
EXECFLOW_OK
Fri May 18 15:49:56 2007 Job 'Rip - title #1' finished
Fri May 18 15:49:56 2007 Process title #1: 20% done.
Fri May 18 15:49:56 2007 Rip selected title(s) / chapter(s): 20% done.
Fri May 18 15:51:08 2007 Project file saved to
'/home/timmy/dvdrip-data/jool-holland/tmp/backup.rip'
Fri May 18 15:51:08 2007 Job 'Rip selected title(s) / chapter(s)' finished
Fri May 18 15:51:08 2007 Job 'Rip selected title(s) / chapter(s)' exited
with error: Job 'Process title #1' failed with error message:
Job 'Process preview frame - title #1' failed with error message:
Job 'Grab preview - title #1' failed with error message:
transcode can't find this frame. Try a lower frame number.
--------------------------------------------------------------------------------

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Fri May 18 15:51:08 2007 Job 'Process title #1' finished
Fri May 18 15:51:08 2007 Job 'Process preview frame - title #1' finished
Fri May 18 15:51:08 2007 Job 'Grab preview - title #1' finished


thanks in advance!

cheers