I had the same issue recently... I talked with Sony and they gave me three suggestions:
A. Do a "hard" shut down by pressing and holding the power button and volume up. (that didn't work for me)
B. Reset the phone by pressing the button next to your sim card. You will need a pin or something small to press and hold the button till the phone resets. (This worked for me for like an hour and then i had the issue again).
C. The final way was following these steps using the Sony PC Companion (this has been working for me the longest so far, just steps 1-11):
**UPDATE**
About an hour after I had done this I ran into the error again... I talked with one of the Sony Reps again and they said you have to send the phone in....
**NOTE** Do a backup of your phone first using the Sony PC Companion or have everything backed up through your Google Account because this way will clear your phone and reinstall the update from scratch through your computer. You will have to let your phone sit awhile afterwards to reinstall apps and updates and you will have to reorganize your phone as well once this whole reboot is complete.****
Download PC Companion from the Sony website if you don't already have it.
Run the software and install it (the Sony PC Companion)
Turn the phone off and disconnect it from the computer
1. No matter what the program says do not connect the phone until you complete step 9
2. In the welcome screen you will see the different modules available for you including the "Support Zone" option. Click on "Start" below it.
3. On the next page Click on "Start" under "Phone Software Update"
At this point if you get an error stating that "Unable to install update components" or "Server is busy" , then please proceed to step 12
4. The program will say that there is no phone connected. Click on the option below that reads: "Repair my phone" the program will issue you a warning about the content that you will lose during the update
5. Choose the option to continue.
6. The program will issue a final message warning you of possible data lost during the update. Click on the checkmark and then on "Next".
7. After that, the program will download the necessary information (5 to 6 minutes) and it will present you with a list of phones.
8. Choose your phones model from the list then click on "Next" then you will see a new section telling you how to connect the phone. (don't connect it yet)
At this point the phone must be off and disconnected from the PC.
9. Connect the cable to the PC not to the phone, then while pressing and holding the indicated button (in the steps on screen an specific button will be shown for you to press on the phone) connect the cable to the phone and keep holding the indicated button until the program says "the update of your phone has started..." (in some cases a message of "Installing drivers" will appear before the message of "the update of your phone has started..." is shown.)
10. If you failed to follow the steps correctly the phone will turn on and it will request that you "Proceed with the following steps, slide down the notification bar", If this happens disconnect the phone from the cable, turn it off and repeat from step 9).
11. If the phone is connected properly, PC Companion will proceed with the update ( It will tell you to let go of the back key) then wait for the update to finish and follow instructions on screen to disconnect the unit.
Dear Customer,
12. If "Unable to install update components"
1. Close PC Companion
2. Install Java from their website
3. Start PC Companion again and try to do the software unlock process once more.
Note: If you wish only to update the unit wait for the program to open and then select the quick link on the upper left corner that says "Update Phone/Tablet" and follow the instructions to perform the update. (the PC may request for the phone to be placed in Mass Storage mode. Do this by going into Settings>Xperia>Connectivity>USB connection mode)
D. Just found this on the Sony Forum. Im trying this now to see if it works:
From reddit user FishStik5: Going into the APN settings and changing the APN protocol to iPv4 only (it was iPv6 before) seems to fix the problem.
How to find the setting: Settings-> Wireless and Network / more -> Mobile networks -> APN -> T-mobile data -> APN protocol -> Set to IPv4.
This appears to fix the issue for me.