The errors will be in the log. If you don't know where that is, read the FAQ post called "Getting to know Eraser 6". If you are using Eraser 6.0.x, it might be flagging up errors that aren't in practice errors at all (Joel has changed the categorisation a bit in the development version).
Erase time is a function primarily of the amount of free space being erased, drive (that is drive plus interface) speed and the number of passes. For erasing free space, use a single pass method. Al;so, disable antivirus and other background programs to reduce the number of disk accesses during a free space erase.
Without knowing more details of your setup, it is difficult to be precise about why the erase is taking so long. On my desktop machines, I would expect a 1TB erase (single pase) to take hours rather than days.