Thread problem

Hi all
I am doing a long code processing includes loops and so on
the problem is the user interface seems to be stuck(not responding) and
this makes the program seems to be hang inspite of it is running well
how can i make the user interface works normal (as i am writing some
instructions for the user but it doesn't appear)
some one suggest to make thread and i did
i put all the code that i process (on timer) inside one function but
when i run the program now i got an error
'object reference not set to an instance of an object'
and i have many function within that code i can't get or debug this
error
any idea??
and do the thread have any special treatment when dealing with objects ?