Try to modify the AdditionalLibraries folder like this:
Create an AdditionalLibraries folder somewhere else and add one subfolder for each product.
B4X is the subfolder for B4XLibraries.
I added a B4XlibXMLFiles for xml files for B4XLibraries.
Put all B4J additional libraries in the B4J subfolder.
The error you encounter is related to a bug in v7.31. It happens when you use the "old structure" for the additional libraries and the folder name ends with B4J. Just change it to B4JAddOnLibrary and it will work. Though it is better to switch to the new structure.