I'm a LPR, I filed I-130 at TSC on behalf on my unmarried, over 21 son in Nov 98. I got a receipt back and a file number. Why is it taking so long for the approval? I've written requesting status.
What else can I do?

Your son is in the second b preference category. You have to wait until a visa number is available for him to come here.

According to the state department, in the TSC they are processing the 2b from 1994.

http://travel.state.gov/visa_bulletin.html