This means that we could not create the parent directory of the target file from the Acceleo engine. This usually boils down to one of :
- the "target" you specified for your generation is read-only,
- the "target" you specified for your generation is owned by another user as the one that runs the generation, and the latter does not have writing access to it, or
- there is a forbidden character in the patch you specified.
"forbidden characters" are dependent on the OS you're running, things like "?", ":" ... You can try and print the full path before you generate it in order to debug the root cause of this issue. Something like :