If you look at your PC's Device Manager, each Hard Drive hanging on the Mobo's PCI(e) bus connected IDE, SATA or USB controller, has several settings in Properties - Options (they are called differently depending on OS version): like optimize as Internal or Removable, Synk Data Transfer, DMA, etc. These setting determine how data flow btw the Proc - PC's memory buffer - HD's memory buffer - HD Heads is controlled by the PC and HD controllers. If there is processing speed & data flow mismatch and the memory buffers are not large enough to handle it, the device will register error and hang.
AZBox is in essence a lower end PC. Its obvious, AZBox firmware doesn't handle this data flow control well for some drive models. Are there any similar settings in its UI regarding removable drives that one can change? Just look at your PC Device Manager and compare your HD settings to AZ UI settings choice for hard drives... Try to play with them, or possibly look on the web for extra related FW plugins.