Error 240 when updating to Radio 1.50
I've been toying with recent radios (I keep getting that annoying "!" to indicate signal ever since I left my old radio). I'd like to try 1.50, but whenever I try to update with the pre-packaged RUU, I get a "Error 240: File Open" message. I tried to use CustomRUU to just use the .nbh, and CustomRUU does the same message. I unlocked my ATT device, which, I'm quite certain, installed Bootloader 1.40. I'm quite at a loss!
How do I get rid of that annoying message and update my radio?