I recommend you upgrade to ROBOTC for Mindstorms 1.10, which is currently available on the website. This is a free upgrade and has greater string/display capabilities than 1.05 has.
Your code doesn't seem to work in 1.10 because it's expected a type "compileConst short" for the variable, whereas you declared a type "int".
This is a bug and I'll take a look at making the DisplayString take an int as well... but in the meantime you can try this:
ROBOTC Developer - SW Engineertfriez@robotc.net