After upgrading to CRM 4, client connections are refused when use the default http:/crm address.
The server resoves it correctly.
On the clients however the only address that seem to work is IP.
Using http://x.x.x.x/organizationname/loader.aspx
A<.
your options are
http://server/organizationname
or
with IFD:
http(s)://organizationname.domain.tld
you could make a redirect for crm.domain.tld