Make sure that you check the box next to "GPIB" on the second screen of the instrument wizard. Also, make sure that what you are seeing in Measurement and Automation Explorer (MAX) is the most recent case (refresh your screen). It is possible that the instrument is offline, but since MAX doesn't automatically refresh everytime a change is made, it may appear that the instrument is still being detected.
The following link may help.
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/8e2f0a10f99519268625680400644435?OpenDocument
Kim L.
Applications Engineer
National Instruments