Make a new post whatever you want ... then after you click submit new thread --- click on thread tools - edit thread - in the address bar is the # you need .. for example
www.whatever/forums/postings.php?t=23736&pollid=
the 23736 is the number you use in the force thread ..
click add new thread ..
add the # you located earlier ..
select if you want the force read to expire or not , if yes select a date ..
Highlight any users that you want force them to read the thread ..
Click save ...
It will work .. It took me awhile to figure this out too ...