Just my guess, could be isolated to Seagate External?
I am using Buffalo 3TB external and no problem at all with the A200. Same thing goes with 3TB internals connected via 3TB compatible docks.
If no good talaga ang Seagate External, then just remove it from its case and use a 3TB compatible dock or replace the case with one that is duly certified to be compatible with 3TB HDD - reformat to NTFS.