Managing audio source does not show score but white area

Hi,
when attempting to manage audio sources of my score I only see a white empty area instead of the score.
This is a score created with version 3 and it used to work just fine. I loaded it with the latest v4 and re-saved it but it did not help.

Tryed with Chrome and Edge browser.
Does anyone know what the problem is?

Thanks for any help on this

Ferdinand