There's an issue with OpenSCAD when saving a file that is located on a Dropbox folder. It claims that the "file is being used by another process" which is clearly Dropbox.
This happens whenever you add sufficient code to add a new object to be rendered/previewed (e.g. cube) and then saving the file. I've repeated the issue on both Windows 8 and 10, on version 2015.03-2.
This is a mild inconvenience but it would be great to have this fixed.
I think that's https://bugreports.qt.io/browse/QTBUG-57299 - probably not much OpenSCAD can do here.
Alright sounds good. Thanks.
Closing as upstream Qt issue is closed. Should be fixed in Qt5.12 (version used in OpenSCAD is shown in Help -> Library Info).