Powershell startup scripts fail on Windows 8.1 with error 267

Question

GPO Powershell startup script fails to execute on Windows 8.1, but does run on Windows 8 and Windows 7. Powershell logon scripts run normally on all versions of Windows.
The event log contains entries with event ID 1130 from the GroupPolicy source. The log entries claim error 267 "directory name is invalid".
Running cmd.exe on Windows 8.1 under the computer's account (NT Authority\SYSTEM) confirms that the Powershell script's path in SYSVOL is valid and the script executes normally.
Running procmon on Windows 8.1 while the startup script is being run on a computer shows that the computer caches the files and folders for this GPO into C:\Windows\system32\GroupPolicy.
I am not sure why these scripts are failing to execute on Windows 8.1 when they run on Windows 8 and the same set of GPOs are applied to both Windows 8.1 and Windows 8 computers.

Answer 1

These are all good suggestions, but I have already tried to eliminate:
All environment variables
All network paths
Setup the GPO to reference the script by the file name and with a full absolute path. Neither worked.
Tried copying the scripts to multiple folders inside the policy, since the event log message reports only the root path of the policy.
I also used procmon to monitor how the computer handles the startup scripts. I found that the computer caches them into a folder under C:\Windows\System32, but never runs any of them. I never found an error that I could correlate with the event log.
For instance the following one line scripts failed to run:
'I AM HERE.' | sc -path C:\Windows\TEMP\TEST.txt
write-host 'I AM HERE.'
As far as I can see the first script relies on the existence of C:\Windows\TEMP and write permission to it, which SYSTEM should have.
The second one liner has no dependencies at all and it doesn't run with the same error.
I have created multiple GPOs and scripts, so if there was a problem in creating these files and folders it is happening over and over. I checked the permissions and computer accounts have read and execute permissions all throughout the GPOs.
Everything works perfectly on Windows 7 and 8, just not on 8.1.