That is the message I kept getting when I tried to open a distribution list under one of my public folders in Outlook.
Clearly the client (Outlook 2003), and the server (Exchange 2003) had plenty of memory, lots of drive space. So I knew that could not be the problem. I thought a nice reboot would fix it.
Rebooting did nothing. So I searched google with that error message. The first result was pointing to Microsoft KB article 894530. This is a hotfix…a software patch you need to call MS for. Got the hotfix, installed the patch, and bam…still getting the error 
I started looking more closely at the KB article, and this line caught my attention:
Consider the following scenario. You use a Microsoft Outlook Web Access client computer to add a new contact to a distribution list. Then, you use a Microsoft Outlook client computer to open this distribution list. In this scenario, you may receive the error message…
Hmm. I never used OWA to access the list. In fact on this server I have *never* used OWA for anything. So I thought why not try to access the distribution list from Outlook Web Access and see what happens.
Wow. It let me in. I got an error message stating that there were 7 unresolved items. I looked through the list and found 7 items marked in red that had no info attached to them. I deleted all 7, and then opened Outlook 2003.
Smiles all around…I can see my distribution list again. No maddening error message. Beautiful.
Now the question is. How did I get those 7 unresolved items? I still don’t know. To be safe I am making sure my backups are running smoothly.
{ 6 comments… read them below or add one }
I was able to Open the distribution list from OWA and deleted unresolved address, but I still can’t open it from Outlook 2003 or Outlook 2007.
You may need to trim down the number of items in the list. This is another reason for the error. Take the Distribution list and split it in two. Put half in one and half in the other…you should be able to open them both after that
I had this same problem, with my DL not opening because of memory. i was able to open it and edit it in OWA. After making it a little smaller by creating a second list, i went back to my normal out look and was able to open both lists. Thanks for the tip.
I have been having the same issue when I use Outlook 2007 but staff still using Outlook 2002 can still open the group ok. I will try access via OWA see if I can see any unresolved items (never heard of those before) seems silly having to open a remote desktop connection with an old version of a program each time i want to use it.
Thank you so much for this solution.
Worked like a charm. I had no unresolved entries, all I had to do was open it up in OWA, add a new entry, close it, and re-open via Outlook client. Issue resolved.
hi steve. my team is facing the same problem while sending the emails to about 19k clients. ill give this solution a shot.