Found that the reference within the block is 'fixed'. So after renaming / relocating you have to recreate this reference. I don't know how to do this 'properly' but I have found a workaround.
- Create a copy of your existing image which is not loading
- Within the mask create a 'new' drawing in graphical mode and save this under the desired name
- Close Matlab/Simulink
- Open the existing image within a texteditor and copy everything
- Open the new image (from step 2) within a texteditor and remove everything
- Paste the code copied from step 4 and save the file
- When you now open Matlab/Simulink, then the original image should be visible again.
If anybody knows were to 'find' this reference and/or to reload this, then I am still interested how to do this. Please leave an comment/answer then.
Regards
Ludo