Sometimes security settings prevent processes from executing from C:\Temp, and this interferes with Altiris Run Script tasks which execute from C:\Temp.
Resolution
Use a Package Delivery task (or Quick Delivery task or Managed Software Delivery policy) instead which will execute from a folder under C:\Program Files\Altiris\Altiris Agent\Agents\SoftwareManagement\Software Delivery.
Copy the script from the run script task and then paste it into a text file and save it with the appropriate extension such as .vbs for a vbscript.
Go to Manage>Jobs and Tasks, right-click on any folder, select New>Task>Software>Package Delivery.
Click *New on the package line then click +Add in the Add or Edit Package window
In the Open window browse to the script file created in step 1, select it, and click Open.
Give the package an appropriate name and enable Automatically generate command lines when package is created, then click OK.
Give the package delivery task an appropriate name and select the command line that was automatically generated, then click OK.