Make sure your anti-virus software isn't interfering.
It's trying to use the C:\Windows\Temp folder, which seems a bit odd because this folder is typically locked down to the system and administrators. It's not necessary or recommended to run Mod Organizer or Skyrim as an administrator so make sure your TEMP and TMP environment variables are pointing the correct Temp folder (usually something like C:\Users\<username>\AppData\Local\Temp) or that you have full access permission to C:\Windows\Temp.
You might also check (in Mod Organizer) Settings, click the Plugins tab, select Fomod Installer in the list, and make sure enabled and prefer are both set to true. This may not have anything to do with this issue, but it doesn't hurt to check to make sure it isn't disabled.