Hi, a quick and dirty workaround could be checking if export succeeds using https://www.nitrc.org/projects/visualign - VisuAlign is the next-step tool for QuickNII, allowing nonlinear deformations. However until nonlinear deformations are not in place, it just creates the same kind of output what QuickNII would. It's done via using "Export..." from the File menu.
I will try to look into the issue with QuickNII, thank you for reporting.