Do you]ve Exchange 2010 and you face an issue where your Outlook clients stuck on connecting status when they try to download OAB through web distribution? It seems this's a common issue and I found that this'll happen if you configured IIS redirection to simplify you OWA URL. After configuring IIS redirection, IIS will create a small web.config file under your OAB folder with the IIS Redirection set to False, issue that outlook clients will try to access this file since it's under OAB folder and since Authenticated Users don't have Read access to file Outlook will get stuck trying to download OAB.
So to solve this issue, just grant Read Access to the Authenticated Users on the web.config file and outlook will then works perfectly. Note: Don't delete the file since IIS will enable the redirection option on the OAB virtual directory and will break the OAB downloads.