I have the WU-1a wireless mobile adpater and found it stops working randomly. Many others have expressed the same problem on the internet. I found a solution so I thought this may help: set your smart phone to airplane mode and it works reliably.

In this mode wifi and BT are shut off.Lock

In iOS you can turn wifi back on after you go into Airplane mode.  This leaves the cellular radio off but wifi on.  I had pretty much given up on the wireless connection to my d7100.  But I gave this method a try anyway.  Not perfect, but much better success than I have had previously.  Enough to go from unusable to usable.

With my Galaxy S3 set to airplane mode, the WU-1a wireless mobile adapter works flawlessly. Only issue is that it drains the battery quickly.I used to get the error message "internet connection too slow" even when signal strength was very strong. With airplane mode, this error message goes away. I guess the problem was with maintaining two simultaneous wi-fi connections.I don't need to switch on airplane mode when I am outside the range of another WI-FI in order to get the WU-1a working reliably. This confirms that the problem is with the phone not the WU-1a.Another helpful phone setting is turning off power savings. Because when the phone goes to sleep your WU-1a cannot communicate with it.Keep in mind that both these settings are at the expense of battery life.

Thanks for the tip.  I will give it a try.  Another beef I have with this app is that it doesn't convert RAW to JPEG for you when you download pics to your phone.  This would allow me to post straight to FB or something when I shoot RAW.  I would hate to have to shoot RAW+JPEG just to do this.

I did not know how to get a wifi signal in once in airplane mode as it shuts off wifi. But indeed, I can reactivate wifi separately. Thanks for the tip.Lock

Having to shoot RAW + JPG just for this? I hear you on that one. Isn't practical. I always shoot RAW + JPEG for another reason. JPEG files are faster to view. It takes my computer a split second to go from one JPEG to the next, whereas it takes several seconds to go from one RAW to the next. Hence, I use JPEG to view and select which ones to keep then I edit with RAW. Fortunately, the D7100 has two slots which makes this an easy process.