I am running yellowfin on XP Servicepack 3 and on vista Service pack 2.. I tried many times to produce your problem without success. (maybe that is good for me).
1) What operating system are you using?
2) what service pack?
3) What other programs are running?
4) What size memory is the computer? .
5) Have you tried to delete YF and reinstall?
Just some things to check...... chuck