Redmine

I've created a forum entry for a project. Since it's the first one, Redmine only has 1 forum entry associated for the project, the tab Forums displays - wrongly - that there's no data to display.

When you have only 1 forum, Redmine displays its message list when you click on the Forums tab rather than the forum list (since you have only one forum, the forum list would not be very usefull). So you see 'No data to display' because there is no message in your newly created forum.

But now, when I enter a forum with topics (and messages) the result is still No Data to Display.

I'm not sure to understand your problem. This seems to work fine for me.
Could you attach some screenshots please (forum list and message list) ?

I'm not able to reproduce this problem.
Could you run Redmine with log level set to debug and then send the log generated when you get the 'no data' message ?
Does this problem occur with the 2 other forums ?

Oh, and please give your ruby, rails and database versions.