>> This happens when a file is corrupted or in a "too new"-format.
>
> There are 2 CAB files -- data1.cab and data2.cab -- apparently this means they are InstallShield CAB files, which are a different structure than Microsoft CAB files. I guess IZArc cannot handle InstallShield CAB files?
Apparently. Maybe another free zipper like tugzip or zipgenius will work: