Got the following via the Harrison R&D OBD-II scanner:

p0420 Catalyst System Efficiency Below Threshold (Bank 1)

The scanner was not able to clear the code.
History:
Bought van 2/2004 with 97450 miles. Carfax report said that "Vehicle serviced Catalytic converter repaired or replaced" 10/01/2003 at 96810 miles. Then it passed emissions inspection. Replaced the fuel pump 12/2004. After driving about 500 miles the p0420 light came on

My questions are:
1. what does the code mean?
2. is it possible to repair the catalytic converter?
3. why could the scanner not clear the code?
4. can I use fuel cleaners first, then try to clear the code?

Thanks