Are you using ArcGIS App from AppStore? And trying to add mentioned server?
If yes, you cannot add that server. The option in the App to add ArcGIS Server is for ArcGIS Server Mobile Content Server. Also, you get it with ArcGIS Server 10.x only.
Nimesh is correct. The referenced services is 9.31. Noting any of the MapServer Supporting Interfaces within the link (http://geoportal.abudhabi.ae/rest/services) do not contain MOBILE, which it must. ArcServer10 using Mobile/Content is required. (or using ArcGISOnline)
