If something's not broken, why fix it? If sulfasalazine (Azulfadine) worked for you before and Asacol is not working, why not ask your doc to put you back on it?
Sulfasalazine is considered to be the drug of choice by Elaine Gotschall, developer of the Specific Carbohydrate Diet, for UC and Crohn's colitis. Alot of folks who've had problems with Asacol favor it - I'm one of them. Here's an article you might find interesting:
Diagnosed with ulcerative colitis spring 1999
C-scope confirmed UC diagnosis 9/18/2007
No explanation for right side pain and thickening of bowel wall
Maintenance dose sulfasalazine, back on a pred taper for first flare in years
Probiotics, l-glutamine and fish oil caps. George's aloe vera juice and Mucosaheal.