It is not uncommon to call external systems to get datasources and the related external fields (Columns) for field mapping.

If an unhandled exception occurs in IExternalSystem.Datasources on a form that is put in as content on a page it will crash the site (process). 

To replicate:

1. Implement working IExternalSystem and select it on a form.
2. Put the form on a page (drag it into a contentarea)
3. Introduce exception in the Datasources getter
4. Watch it explode (process crash is serious and will probably make a site unresponsive, which of course is dependend on where you have put the form)

To quickfix:
Put try/catch around the logic and just return IEnumerable<IDatasource> in case of exception.

Will also sent email to support