There was a problem downloading [Movie Title]. An unknown error occurred. (-50)

Just got LOTR: Trilogy Extended Editions on Bluray for Christmas and went to redeem the Digital Copies in the iTunes store. Codes worked fine, they have been successfully redeemed.

Only problem is the movies will not physically download to my harddrive and I get this error.

I have done the recommendations and step-by-step guides on this page: http://support.apple.com/kb/TS1583 many many times but to no avail.

I've heard that sometimes Digital Copies require you to have the DVD or Bluray in your DVD or Bluray drive before they will download but if this is the case I haven't once been prompted to insert any such disc.