First check that there is something in your tag file. If you followed the instructions on the page you mentioned, it should correctly define classes, methods, etc. If this worked, you can go to the next step.
taglist plugin has a hard list of supported language settings, and Scala is not one of them. Therefore, even if CTags generates the correct tags, the plugin will not read them for this type of file.
It should be possible to add a definition as a global variable g:tlist_def_<lang>_settings, but I could not get this to work. Therefore, you need to modify the taglist.vim file in the directory ~/.vim/pluginto add Scala support. Do not worry, it is easy to do!
Find the line that defines s:tlist_def_yacc_settings, and add the following lines after it:
let s:tlist_def_scala_settings = 'scala;t:trait;c:class;T:type;' .
\ 'm:method;C:constant;l:local;p:package;o:object'
, Ctrl-T, Scala .