Failed to save target/IDML file

Hi, I've just encountered the infamous error message "Failed to save target content: Value cannot be null. Parameter name: value" when trying to Save as Target. I'm translating an Indesign/IMDL file in Studio 2014 sp2. I tried saving as target after just starting the job, which worked fine. Now I'm worried I won't be able do deliver as planned. Can anyone help?