Hi Pål,

I had a similar problem and solved it by using a UserAuthorCriterion to filter on the User attribute:

UserAuthorCriterion criterion = new UserAuthorCriterion();
criterion.User = new UserCriterion();
criterion.User["Attribute"] = new IntegerCriterion();
((IntegerCriterion)criterion.User["Attribute"]).Value = attributeValue;

TopicQuery topicQuery = new TopicQuery();
topicQuery.Author = criterion;

Maybe there are other ways of doing it but this seems to work fine for me.

Best regards,
Helena