TrueCrypt mount fails with cryptic error

Solution 1:

In the end, I did not find a way to make this work under OS X. I copied the file to a Linux machine, mounted it and then scp'd everything to my OS X running machine. Reasonably simple but takes some time and one needs access to two machines.

Solution 2:

Try mounting the volume as “read-only”:

TrueCrypt → Preferences → Mount Options → Mount Volumes as read-only

If that doesn't do the trick then it's possible TrueCrypt could be having some issue with file system implementation mechanism (ext4fuse) not detecting that an ext4 volume is mounted. I've used FUSE for OS X with TrueCrypt and it works without any issues, so giving that a try instead of your current mechanism might help as well.

Solution 3:

Try selecting "Do not mount" in VeryCrypt and then mount the disk manually. Open terminal:

diskutil list
/dev/disk5 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            VERACRYPT               +10.2 MB    disk5

diskutil mount /dev/disk5
Volume VERACRYPT on /dev/disk5 mounted

There seems to be a problem with FAT32 and exFAT filesystems. After manually mounting the volume, I created a new with HFS+. I was able to mount it without any problems. I'm using Mac OSX High Sierra.