The username to access Lancet online via thelancet.com (this is the second link listed in the MNCAT record) should be Biomedlib, with a capital B. I have notified the powers that set up the proxy URLs so hopefully this should be fixed shortly. There is also a problem in accessing the username/password through SFX, so try to use the MNCAT link if possible.
If you have any questions let me know.
Nicole