I have a problem saving a part in Solidworks 2016 sp0. It has happened twice, with different parts.

The problem is that I can not save the part, and if I want to "Save as" with another name, it creates a 0 kB archive. I just can not do anything but starting to draw it from the beginning. The last time that happened, I inserted an existing part inside the new part, and I figured that the problem was in that feature, but it was impossible to delete the feature and save the document.