HMMM .....
"C:\Windows\TEMP\Serviio\ is not accessible" this little cryptic bit of info is very suspicious.....
Try assigning a different file as a Serviio temp file for transcoding. This works well in Linux ..I see no reason why this might not also work with Windows.

- serviio using a different tmp in Linux
- seviios.png (28.23 KiB) Viewed 4718 times
The reason for this is access permissions, Windows settings and A/V software can sometimes block access for programs to create a sub directory in \TEMP and not tell the user why. If Windows or A/V software thinks that Serviio requires admin access to create a TEMP\Serviio directory then things can get confused. If you are using WIndows as a limited user then this can cause non specific user access permission problems.
In Linux the same problems can also occur and this is why I install Serviio as a non privileged user, then reset the tmp file that Serviio requires for transcoding to a current user profile. I am experimenting with doing the same setup with Windows. Remember that network access restrictions can also sometimes cause things to not work even though the program is working correctly.
Try shutting down Serviio and then right clicking on the startup and running Serviio as administrator. If this allows Serviio to create a directory in TEMP then read and write to it then this is the problem you are experiencing.
In Windows the use of \TEMP should not require administrator privilege ...but it can happen with a setup that has limited user privilege like with Server 2008 and any Windows install that has been setup to block users or user installed programs from writing temporary data to C\windows sub directories other than the current \user.
Even some firewall settings can block programs from creating sub directories..but there should be some indication that this has occurred. Unless warning have been disallowed and the security settings are set to not allow the creation and use of directories within C:\ or C:\Windows ....however there should be no problem having Serviio read and write to a \current user directory that you select as a user even if no other user can access this created \TEMP\Serviio directory.
If I remember correctly not allowing programs to create temporary directories is one of high security settings of Windows Security Essentials, McAfee, Norton and Kepersky A/V software
User and program access permissions are an ongoing problem and can be really frustrating to resolve... I hope that this is a simple situation and is all that is happening.