Update:
This is no longer needed if you are using the UDGP, as the relevant bug has been fixed. See forum for details: Mods Made Obsolete by Unofficial Patches

This isn't needed by 99% of players out there, evidenced by the lack of fixes found on the interwebs.

Essentially, some players find that Auriel's Bow stops affecting the sun. Bloodcursed and sunhallowed elven arrows no longer produce eclipses or sun flares, and no visual effect occurs when looking at the sun with arrows and bow equipped. Needless to say this is frustrating when you play as a vampire.

The download includes a bat file named aurielsbowfix, which when downloaded can be renamed to whatever you want and placed in the Skyrim directory. In-game on whichever save file you're having issues, open the console and type "bat aurielsbowfix" or whatever you renamed it to. This will remove and re-add the ability, allowing use of the bow's special effect again.

If after using the bat file you still can't shoot the sun, drop and pick back up the bow and arrows. You don't need to add a new bow via console or avoid tempering it, the fix will work regardless of tempering or replacement bows.


Fun facts:

Your Elder Scrolls are useful and should not be sold!
Elder Scroll (Sun) and Elder Scroll (Blood) can end the eclipse effect prematurely, in case you're planning to visit a city and don't want a chance of a vampire attack, or you want to use Sunhallowed arrows.

Also, reading one will kill your thralls. Fun punishment for their incessant moaning!

Last, they're a lie. That's right. The background isn't stars from Tamriel's sky. It's from Earth's.