Diagnose input/output errors on a Truecrypt container

I have been trying to get a local repository located on a usb drive working on an air-gapped machine. The repository was created with apt-mirror on the same kind of system (ubuntu i386). Currently I am blocked by being unable to scan the packages on the usb drive. This is what happens: cd /media/truecrypt1/apt-mirror/mirror/archive.ubuntu.com sudo dpkg-scanpackages . /dev/null | gzip -9c > Packages.gz bash: Packages.gz Input/output error dpkg-deb: error: error reading archive magic version number from file ./ubuntu/pool/main/libm/libmaa/libmaa-dev_1.3.1-1_amd64.deb: Input/Output error dpkg-scanpackages: error: couldn't parse control information from ./ubuntu/pool/main/libm/libmaa/libmaa-dev_1.3.1-1_amd64.deb What could be my problem here? How do I diagnose an input/output error on a TrueCrypt container?