This should work within Automise. Running the test here works well, as there is nothing else accessing the file. Could there possibly be something on the machine that has the file open?
No nothing has the file open. If I simply move the action out of the Async group it works. But I also see that if I write to another folder (a subfolder in the same folder of the Automise project) it works. Could this be a rights issue? I am testing it on Windows 2012 R2. I will look further into it.