Opening OAB in Outlook or Outlook Web App – generates an error

Here is the problem:

When your users is trying to send a mail, by pressing To: within a new mail they either sees a blank screen (Outlook) or an error in Outlook Web App saying:

Exception Exception type: System.NullReferenceException
Exception message: Object reference not set to an instance of an object.

This is the solution i used to fix it:
Open ADSIEDIT from any Windows server 2008 or above
Connect to Configuration and go to CN=<Organization name>,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=<domain>,DC=<extension>

Right click <organization name> and select properties, go to this attribute MSExchResourceAddressLists

look for entries which says something about deleted objects, mine said 
CN=ALL ROOMS\0ADEL:6bcdde75-73a5-4b67-9fd5-79e9fa43d805,CN=Deleted Objects,CN=Configuration,DC=<domain>,DC=<extension>

I deleted that entry, restarted IIS using IISRESET /Noforce – services hangs, but could be manually started after a couple off minutes.