I had this problem but I managed to kill the temp.exe process (once I figured out it was the one I should kill).
is temp.exe running? (check from process monitor, make sure it's showing all processes from all users, just in case.
does temp.exe have write permission? maybe construct is unable to overwrite it for some reason.
It happened me once with a runtime crash where temp.exe got stuck and I couldn't run any more previews. Again, as said, killing it made everything go back to normal.