TAPECOPY function should not be used when changing media-types and FILECOPY should NOT be used when copying data that from an application (CA-Dispatch) that keeps track in their own database of the volser and block-id information.
Block-id is VERY different between a 3480/3490 device and a 3590 device. A block-id on a 3480/3490 device is a 3-byte value; and on a 3590 device it is a 4-byte value, which is completely different. If the application (CA-Dispatch) has a 3-byte block-id stored; and tries to use it to position itself on a 3590 device – it just won't work.
The block-id value that is stored by the application will ONLY work on the same type of device.
Now, using Copycat to do a TAPECOPY from one 3490 virtual-tape to another 3490 virtual-tape would be just fine; since the 3-byte block-id would be the same for both.
But going from a 3490 virtual-tape to a 3590 virtual-tape is COMPLETELY different.