We recently migrated our email system from Exchange 5.5 to Exchange
2003. Some of our people have a shared contact list that has around
800 entries in it. In the 5.5 system this was in a Public Folder.
They would do a "select all" - "new message to contact" and send their
message.

On the new system, when they do that they get an error that says, "The
custom form could not be opened. Outlook will use an Outlook form
instead. The operation failed."

I've found if there are fewer than 250 entries in the contact list,
the error is not displayed. This seems to be fairly consistent. It
doesn't matter if the contact list is in a Public Folder or shared
from a mailbox. The client in question is Outlook 2003. By the way,
if the same contact list is copied to a mailbox, the "select all" -
"new message to contact" works just fine with all 800 or so entries.

I've cleared the form cache, as was suggested in several other posts,
but it doesn't make any difference. We are not using any custom
forms. Before I get too far into this, is there a set limit to the
number of entries in a shared contact list?

Thanks.