Hi!
Here's the work-around.
First, the problem: if UWS was installed on Windows 8, or 7, and then upgraded to 8.1, 8.1 installer re-ACLs ASP.NET temporary files folder by revoking write access for Network Service user.
To fix the problem, please
grant "Network Service" user write access to the following folders:
C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files
C:\Windows\Microsoft.NET\Framework64\v2.0.50727\Temporary ASP.NET Files
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files
If any of the listed folders don't exist on your system, skip them - it's not going to cause any problems.
In the next UWS build (20) we are going to add re-ACLing to the RegRepair utility so this problem can be fixed by simply running it, or by reinstalling UWS.
Please let us know if this information helped solving the problem.
Best regards,
UltiDev Team.
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http://www.ultidev.com/products/Donate.aspx to help us improve our products.