It sounds like you have a Group Policy at either the Site or Domain level
that doesn't allow you blank passwords. There is a way that you can still
create users without passwords though. The first is to create an OU that
has a Group Policy applied to it that overrides the Domain level policy
(keep in mind, however, that if the Domain level policy has the "No
Override" setting checked, this won't work). With the OU in place that
allows blank passwords, create all users in that OU, and then move them to
another OU. The other way is to disable the restriction at the Domain
level, which most likely defeats the purpose.
David Waldron
MCSE+I, MCP+I, MCDBA, MCSA, MCT
Microsoft Enterprise Support
EPS Directory Services Team
(e-mail address removed)