I fear I can’t say much to help you based on the things I know.. We have over 7000 downloads and it usually just works. I’d make sure there is only one single lead-dbs folder on your hard-drive (delete everything older or so). Make sure you have SPM12 on your Matlab path. Also make sure you have ML version >= 2015b.
If that doesn’t help, do you have a Matlab expert somewhere in your institute who could have a look at it?