Please provide more information such as the brand of your Ext HDD and if it is a single drive unit or a high capacity drive that really uses 2 separate drives along with information about error screen or text. Copying to the PC would be in violation of Dish's agreement with the content providers (Hollywood studios, et al) who didn't want this feature to be made available in the first place for precisely the reason you want to use it: to copy to a PC.
Well, along with a great many other users, I personally have experienced NO problems what so ever since I started using the external HDD feature back in January of this year. The current Ext HDD's I have hooked and/or have on rotating use are an old Maxtor 120GB, another old Maxtor 160GB that I actually knocked off of a table with a big BANG before using it for Dish, yet it still works (a different class from the first Maxtor), and 2 new Western Digital My Book Home Edition 750GB, and all have performed with no problems at all. Furthermore, I've installed a Western Digital My Book Home Edition 1TB at my uncle's for his recordings, and he reports all is great with his Ext HDD.
I have sent to the Ext HDD, and used the Restore feature and done all sorts of commands, as well as start and stop recording, then returned to recording using resume. I've restored recording, then connected a different drive and sent the restored recordings to that different drive, and it works and plays fine. In other words, I have used all the features and really put the Ext HDD through its paces, and it has always worked perfectly.
Given the great number of Ext HDD reports (yes, there are, as with anything, some negative), it would seem that your problems may have to do more with your Ext HDD unit than with Dish Software. There are some problems noted with some Seagates that Dish is aware of and either have or will fix via software.