Back then when I was using Lumia black (8), things seem to be fine.
After updating to 8.1 using preview for developers, yeah I live it very much. But I don't know what happened to my device. I was able to sideload stuff like, you know, install paid app for free. But that was for a while. Now I'm not able to do that anymore. Whenever I connect my device to PC, it keeps on showing device decriptor request failed.
DONT SAY "TRY USING DIFFERENT CABLE OR USB SLOT". I did ask those IT guys about it, but they seem stupid (no offend). All they told me was this line I mention in DONT SAY.
I have 5cables in my house, 2laptops and 1desktop, all with Nokia sdk, with total of 15 USB slots. I tried it all and it's not working.
I wish someone in here can help me since google couldn't. Sorry for my English.