Gnucash 2.6.18 blank screen in macOS 10.13.1

[martin kirby-sykes]

   I have just started running Gnucash 2.6.18 on a MacBook running High
   Sierra after many years of running it under Linux.
   Each time I try to post a transaction the screen goes black.  The menu
   bar is available but inactive. The only way I have found to close the
   program is to force quit in activity monitor.
   Does anyone have any thoughts on what may be going wrong?