I suppose your walls are entities then? You can use EVENT_ENTITY then, and remember to check whether the "you/your" pointer is valid, like this:

if(event_type == EVENT_ENTITY && you != NULL)
{
you.skill1 -= 5; // Decrease healthpoints
}

Edit: if the error(s) you are getting are 'empty pointer'-errors, this might be worth reading:
http://www.nighthawk.dk/v5/index.asp?PageID=ShowArticle&ID=5
It's c-script syntax though, but might still be worth reading