[pptp-server] invalid username/password for domain

[Greg Tibbitts]

I am using pptpd-1.0.0 and slirp-1.1.2 on Solaris 7 for intel. When I
connect I get the following error:
The computer you have dialed in to has denied access because the username
and/or password is invalid on the domain.

The log says:
May 13 08:16:43 ds9 pptpd[6903]: GRE: Bad checksum from pppd.
May 13 08:16:43 ds9 pptpd[6903]: CTRL: Error with select(), quitting

Any ideas?