Erase External Drive

Hard to say - sounds like it is hung up - could be a bad disk/sector/block that it can't get past - there are really no logs to go on or anything else.

There are several free tools that erase hard drives securely as well.  CCleaner is a common one, but if you don't like to have software installed (it's a reg cleaner too - the only one I would recommend, but I can see why people don't like them as I have had bad results with other products in this catetory), there then DBAN is another great one that works great and has a bootable disk that can be downloaded and run without needing to install anything..  

Alternatively, you can also get a hard drive dock/cloner that can securely wipe disks physically, plus it does hardware cloning without the need for a PC and it can act as a dual USB dock when connected to a PC - not bad for a tool that does all of these thigns for less than $40.

Anyway, can't really help with this specific case, but there are lot's of ways to securely wipe a disk and I'd try one of the other free software to see if it also gets hung up or not.  If it does, you probably have a disk issue.  If not, well, then you've found something else that is capable of doing this as well.