I got this error a lot when I did the vocoder change. Did you do the vocoder change?
I have discovered that, in my area, my 3G data service is complete crap (but 4G is pretty close to wifi speeds...I don't get it, but whatever). With the vocoder change, I wouldn't be able to connect to 3G if signal was weak or being interfered with (lots of other electronics around). So it would give me that error repeatedly. I changed my vocoder back to the standard one and 3G would work, my voice quality is pretty good, and 4G is awesome.
I guess my Sprint 3G tower is complete crap in the area, and no one noticed/complains because 4G is so good? /shrug