Update to 10.5.1.A.0.283 fails every time

Question

Update to 10.5.1.A.0.283 fails every time
It is Xperia Tablet Z SGP321, no branding, no SIM lock.
In the past only Sony original firmware were flashed.
Currently 10.4.1.B.0.101 is inside.
Update to 10.5.1.A.0.283 using PCC fails on every attempt.
PCC was updated to latest available version.
The whole progress looks like following
- first PCC carries out the preparation stage
- than PCC reports to carry out download
- as soon as progress bar at approx. 50% of whole scale the preparation stage 
 is entered again
- it takes very long time, between 5 and 10 minutes, till the progress bar reaches 
nearly 100%
- download procedure ends with following message
 error code 10, a hint to check firewall settings if PCC and Sony Update Engine
 are passed through, a hint to retry later
- switch off firewall
- switch off antivirus
- disable all protection mechanism in Windows EMEA
- uninstall PCC, reboot, install  PCC of current version again
All the above measures do not help.
One week ago the Sony Support claimed I should retry some time later.
How long do I have to wait for retry? a week, a month, a year, 10 years, 20 years?
It is a big effort to get this device close to the windows desktop device
with PCC installed and running on it, to get connected this device with such windows desktop device,
to invoke PCC and the update procedure. All this effort just to see in the end the update
does still no succeed!!!!
How long do I have to live with Xperia and obsolete Android on it?

Answer 1

The point of trying a different computer is that it gives information. 
If it works you know that your PC is the problem. 
If not, you have to look further. 
And finally - if nothing works  - you can try to flash it. 
My Sony z is working like reborn after a clean install. 
It takes some time to learn,  but after that it isn't that difficult. 
My tablet works like before KitKat (sd-card) ,  but with the new functions. 
No serious bugs whatsoever anymore.!