libdvdread has trouble with some DVD images

The company I work for has a library of non-encrypted DVD images on a 
large file server.  These images were created as backup copies of VHS 
video tapes using some DVD authoring software.   I've been using tccat 
from the transcode project (which uses libdvdread) to extract the mpeg-2 
streams from these but a small percentage of them cause trouble.  The 
exact error is:

tccat: ifo_read.c:324: ifoRead_VMG: Assertion `vmgi_mat->vmgm_vobs == 0 
|| (vmgi_mat->vmgm_vobs > vmgi_mat->vmgi_last_sector && 
vmgi_mat->vmgm_vobs < vmgi_mat->vmg_last_sector)' failed.

For reference: The Mediamatics DVD player in Windows can play from these 
images.  Also, if I make a physical DVD-R from one of these images, I 
can play it in a Sony DVD player.

Any ideas for how to proceed in enhancing dvdread to be able to handle 
these?

I modified ifo_read.c to dump the contents of the vmgi_mat struct.  Here 
is example of its output:

vmgi_mat_t:
    vmg_identifier[12] = "DVDVIDEO-VMG"
    vmg_last_sector = 277
    vmgi_last_sector = 47
    zero_2 = 0
    specification_version = 16
    vmg_category = 0
    vmg_nr_of_volumes = 1
    vmg_this_volume_nr = 1
    disc_side = 1
    vmg_nr_of_title_sets = 2
    provider_identifier[32] = "FLASH-DVD"
    vmg_pos_code = 0
    vmgi_last_byte = 1275
    first_play_pgc = 1024
    vmgm_vobs = 16
    tt_srpt = 1
    vmgm_pgci_ut = 2
    ptl_mait = 0
    vts_atrt = 45
    txtdt_mgi = 0
    vmgm_c_adt = 46
    vmgm_vobu_admap = 47
    nr_of_vmgm_audio_streams = 0
    nr_of_vmgm_subp_streams = 1
tccat: ifo_read.c:341: ifoRead_VMG: Assertion `vmgi_mat->vmgm_vobs == 0 
|| (vmgi_mat->vmgm_vobs > vmgi_mat->vmgi_last_sector && 
vmgi_mat->vmgm_vobs < vmgi_mat->vmg_last_sector)' failed.