This is normally caused by the site using a HTML5 type player with components that are not supported.
Under Settings > DVR try changing the DVR Browser Type to Browser Control and the Browser Emulation mode to IE 10 Stds Mode or IE 10 Default and try again. This may force the site to use a supported player and it can then be DVR captured.
Please tell technical support about any sites that you find that still cant be DVR'ed.
If the DVR comes out black, try the following.
1. Close JMR
2. Open IE and clear its cache.
a. From the Tools menu (Alt-Shift-X) choose Internet Options
b. On the General tab, under Browsing history, click Delete
c. Ensure "Temporary Internet files and website files" is selected. You can keep "Preserve Favorite website data" select if you wish
d. Click Delete
c. Close IE
4. Ensure IE isnt still runnning in the background
a. Cltr-Alt-Delete and select task manager
b. Ensure no Internet Explorer (iexplore.exe) tasks are running - End them if they are
5. Start JMR and try DVR again