[What's_nitro?]

If your using end-to-end joints, you need to make sure BOTH sides of the joint get soldered. I had some problems with the solder not flowing around the whole wire, even with both sides tinned. In that case only half of the joint's cross-section would be soldered at most. Most likely this would cause localized heating and the joint would fail. The one thing that gets me is that they ALL failed, at the exact same time, too, because otherwise not all of them would have failed.

Edit: LOL. This took a while to write but BrianG has the same idea.