OK - for the marker you have not had the required files in the Objects/res/Layout and Objects/res/drawable folders. When you download and uzip the attached project you should use 7-zip
Make sure the marker1 to marker4 files are in the Objects/res/drawable folder and that their properties are set to "read only""
The same applies to the custom_marker_view_1 to custom_marker_view_4 files in the /Objects/res/layout folder of the B4A project
Have added it to the attached B4A project...the error that you got should now be gone.
View attachment 154039