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Here's the debug log

Debug log started at Sun Jun 17 14:32:34 2012 , written by MakeMKV v1.7.4 win(x64-release)
Using 524544KB for read cache.
001005:0000 MakeMKV v1.7.4 win(x64-release) started
001004:0000 Debug logging enabled, log will be saved as C:\Users\Choque/MakeMKV_log.txt
003007:0000 ...

Here are the compressed IFOs. Thanks for your help so far

Hi!
Actually, MakeMKV prefers to be directly fed UN -mounted .ISO image files instead of mounted .ISO image files...

The same happens when loading the ISO directly into MakeMKV

Please enable debug messages in preferences and post the log.
Here's the Debug Log
Debug log started at Sun Jun 05 ...

When trying to open the DVD "The Last Unicorn" MakeMKV reports this in the log field on the bottom
MakeMKV v1.6.10 win(x64-release) started
Using direct disc access mode
Complex multiplex encountered - 11 cells and 10260 VOBUs have to be scanned. This may take some time, please be patient - it can ...