I think (but not 100% sure) that Sling have removed all Slingcatcher update firmware from their servers, also changed the server addresses. I suspect that your box is now unable to locate the update server (or files on it).
I notice that Kwhit modified your original post, but did not comment or reply. You would think Sling would at least comment, but it seems not.
I have 3 'catchers, currently they are working fine, but am dreading the day when I maybe need to do a hard reset and then they fail to operate ever again.
I cannot understand why Sling does not have an area for legacy products, where there is a firmware download facility. I know that Sling used to email a usb boot operating system to 'catcher users who were having problems, but I have searched for this over many months and have never found it.
Out of all the products that Sling have produced, Slingcatcher coupled with pro, pro-hd, seem to have been the most reliable. If only they had continued to develop the 'catcher! Sad.