Unable to save

I just started using a 2016 Macbook Pro. I installed Igor 6 and upgraded from El Capitan to High Sierra. I can open Igor files but when I save I get the error
"Logical end of file was reached unexpectedly during operation". I get the same error if I try to "Save Experiment As...". Is Igor 6 incompatible with High Sierra? I just purchased Igor 7 and I will try to see if I get the same error. Before I do that, I am hoping someone might tell me a way to save my half-hour of work before I force-quit Igor 6 and install Igor 7.

Pietro