When the software is running as a service it runs using the local system account, which may not have the right permissions to write to that folder. You could try running the service explicitly as the administrator to troubleshoot it but whether that is an appropriate long term solution will depend on your environment.
In order to set the service up to run using the administrator account use these steps:
Start>Run : "services.msc"
Right-Click the service name and choose "Properties."
Click the "Log-On" tab and choose "This Account" filling in your administrator username and password.
Restart the service.
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