Hi Simon,
I assume you are using the AppStore version of Small Basic, this is the only 1.3 version. Unfortunately, this error number is very generic and doesn't suggest a specific issue. Looking at the AppStore review of version 1.3 you are not alone.
Microsoft isn't updating Small Basic and I would characterise both the AppStore and online versons of Small Basic as 'unfinished work in progress'.
I would strongly recommend the desktop version 1.2. While it is also not maintained by MS, it does work well, has a community of supporting users and can be used with extensions that can both extend and fix some issues.
Whatever you try, I would first try full uninstall using 'Add or remove programs' first before a reboot, then install.