No problem here (v11.01)
Just added vector to my workspace tagfile ... (see attachment)
There is no need to add the 'standard' ext.less files as extra ext. less C++ files.
Slick has a default built-in list of them.
One more thing to check: 'Project -> Project Properties -> Compile/Link Tab'
Is the Compiler the right one ?
BTW: A simple way to check if Slick recognizes these files as C- files:
Type e.g.
#include <list> in a C file and move cursor into the word 'list' and 'Goto Definition' using r-mouse context menu or
Ctrl-. (maybe you already know all that ...)
Slick should find it and colorizes it as C file.
HS2