invalid dvd navigation structure?

[Kwark]

I have a DVDR .img (Starwars5) which DVDShrink doesn't like.
It complains about an invalid dvd navigation structure, but the image plays fine with PowerDVD. I don't have access to a standalone atm, so unfortunately I can't check if it works fine there too.

How can I check if there is really a problem with the structure, or if it's just a quirk of dvdshrink?

Get VTS sectores of IfoEdit didn't change/fix anything.
My IfoEdit knowledge is really limited, but can anyone tell me where to check?

[Mr.Shine]

If this DVD has been tampered with before, there might be VTSs missing, so you'll have to adjust the VIDEO_TS.IFO to not reference the missing VTSs anymore. Check how many VTSs are referenced in your VIDEO_TS.IFO ("Number of video title sets on this DVD"). If there are more entries than you actually have VTS_* files, that's your problem. If there is a hole in the VTSs (e.g. VTS 1, 2 and 4 present, 3 missing), you're more or less screwed, since it'd require a lot of editing in the IFOs to move the VTS(s). Holes in the VTS structure are not allowed. If only the last VTS(s) is/are missing, you can simply reduce the number ot title sets and titles in VMG_MAT, VMG_PTL_MAIT, VMG_VTS_ATRT (# of title sets), VMG_PTT_SRPT (# of titles) and probably some other places as well. Make sure not to confuse the title set count and the title count ("Number of title play maps"). They're often identical, but sometimes one VTS contains multiple titles, so the numbers might differ.

This will, however, only fix the DVD layout and get around DVDShrink's checks. If the missing titles are referenced from the command structure, you might end up with an unplayable disc due to jumps to nonexistent titles. If you remove VTSs, you should always adjust all links to the removed titles, either by disabling the buttons that lead there (MenuEdit) or adjusting the PGC commands (IFOEdit).

IFOEdit's "DVD Play" feature usually tells you when it encounters an invalid command (might depend on your installed software player, though). It doesn't tell you WHICH command(s) is/are invalid, so it can take quite a while to find the problem and repair such broken DVDs. VM commands and DVD structure knowledge is required, too.