Hello, Crispin.

Thank you for contacting us.  We cannot tell very much without a better description and, ideally, some data.  Please do this:

• Hold down the 'option' key on your keyboard.
• While holding it down, launch BookMacster.
• "OK" through any message which appears.
• Click in the menu: Help > Trouble Zipper.
• Trouble Zipper will ask you a few questions about whether or not to include additional data.  I do not know if the additional data will be helpful in this case, but if you send it now, I won't need to ask for it later.
• Attach the report it generates to the email it generates.  In that email, plese describe what you mean by "suddenly started crashing".  I mean, do you see a message on your screen using the words "BookMacster unexpectedly quit"?  Also, please explain if there are any particular events you can do to make it crash, etc.