I use sql 2000 for my project and asp.net 2.0 application with membership integrated feature. Suddenly, user to role mapping stopped to work. After a debugiing I found a problem in database layer that caused by some collation incompatibility. I realized the It could be only caused by fact that I use two computers with different sql server collations. I tried to search a web to find solution for this trouble but did not found anything. So the only solution was to rebuild entire database.