Sorry I just posted this issue before leaving on vacation :-)
I'm back now and tried to reproduce the pb for a whole day without success based on your sample.
I modified it to match to the closest the real application but no way :-/
I added two derived based classes Myitem and AnotherItem which does not implement the AllFields field. But it just raise a binding error but not the exception.
I tried to switch the root value in code behind.
I tried to reproduce the workaround used in the application regarding the issue about the changing the CurrnetXPaththat does not fully change the breadcrumb Path itself (only one more level on each call, so we split the path in chunks and call them all on dispatcher !, see this related fix here for silverlight http://www.telerik.com/support/pits.aspx#/public/silverlight/7544
I'm sorry, but I only have access to the exception in logs from the real application, but no way to reproduce and debug it live to figure out what's the cause of the crash.
Could you give me a clue about what causes the crash in the breadcrumb sources ? which field is involved there ? the ItemsSource, the Path ? the Root ?
PS : can't send you back the modified project as a zip archive even renamed as .png < 2mb :-(