I had the same problem with my Icon. It took about 7 or 8 tries (seriously) to get 10149 to install. I'd tried just about everything when I decided to poke my head in the forums here and saw that several people having similar issues resolved the problem by keeping the phone cool during the upgrade. So I stuck mine in the fridge. Here's the steps I went through on my successful install:
1. Restore to WP 8.1 Update via WPRT (had to do this to resolve the looping gears issue).
2. Install all OS updates.
3. Remove any unnecessary apps.
4. Install the Insider app and set the update path to Fast Ring.
5. Let the phone download and prepare to install build 10149.
6. Charge your phone fully (I did mine with ~85% battery and it was nearly dead after).
7. Start the installation. Wait until you see the gears screen.
8. Remove your phone from the charger. Especially if it's a wireless one. They make the phone hotter faster.
9. Keep your phone cool!!! Putting it in the fridge is a little extreme... using a fan, or even placing the phone on a flat, cold, metal surface will probably do the trick.
Someone made a post stating that Nokia built a safety mechanism into the phones which effectively disconnects the battery when the phone gets too hot in order to prevent damage. I'm not sure that's the case, but I did see a battery icon with a question mark several times on failed attempts. Also, all failed attempts displayed the low battery icon at some point; yet when the phone was restored it had over 50% charge most times.
As silly as it may sound, I tried all the steps above - without the cooling part - several times to no avail. Once I kept the phone cool during the update installation everything went smoothly.