m0n0wall Forum - VPN (PPTP) connection problem

I just recently replaced my old firewall with a m0n0wall, and have everything in my network functioning as I want. I also decided to use the VPN server built into the device, and it is working to some extent.

My setup:
LAN network: 10.80.1.0/24
PPTP Server Address: 10.80.1.120
PPTP Address Range: 10.80.1.96/28
No Radius

Here is the problem I'm having:

After setting up the VPN (and also creating the PPTP rule per the m0n0wall handbook), I tested connectivity from three separate remote locations, with three different accounts. The ISP at each location was Comcast, and each location had a basic Linksys router (192.168.1.x). These three connections all worked.

After that, I had a few friends test the connectivity from their own locations. 2 of the three could not connect, and still can't. All locations that were successful still work reliably. The 2 people that could not connect have had their configuration/network looked at by me personally (through vnc), and they have an identical setup to the working connections.

Here is what happens for a user that cannot connect:
Connection is created in Windows (New network connection; VPN)
User enters the public IP for my network.
User enters login/pword (verified many times)
User attempts to connect.
Connection status sits at "Verifying Username and Password" for about 10 seconds, and then displays the following error:

"Error 619: A connection to the remote computer could no be established, so the port used for this connection was closed. For further assistance, click More Info or search Help and Support Center for this error number."

I managed to get the log data that the m0n0wall captured with regards to the failed connection. Please see below:

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Jul 12 08:34:49    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:49    mpd: MP SHORTSEQ
Jul 12 08:34:49    mpd: MP MRRU 1600
Jul 12 08:34:49    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:49    mpd: MAGICNUM 9e646f84
Jul 12 08:34:49    mpd: MRU 1500
Jul 12 08:34:49    mpd: PROTOCOMP
Jul 12 08:34:49    mpd: ACFCOMP
Jul 12 08:34:49    mpd: [pt0] LCP: SendConfigReq #73
Jul 12 08:34:47    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:47    mpd: MP SHORTSEQ
Jul 12 08:34:47    mpd: MP MRRU 1600
Jul 12 08:34:47    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:47    mpd: MAGICNUM 9e646f84
Jul 12 08:34:47    mpd: MRU 1500
Jul 12 08:34:47    mpd: PROTOCOMP
Jul 12 08:34:47    mpd: ACFCOMP
Jul 12 08:34:47    mpd: [pt0] LCP: SendConfigReq #72
Jul 12 08:34:45    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:45    mpd: MP SHORTSEQ
Jul 12 08:34:45    mpd: MP MRRU 1600
Jul 12 08:34:45    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:45    mpd: MAGICNUM 9e646f84
Jul 12 08:34:45    mpd: MRU 1500
Jul 12 08:34:45    mpd: PROTOCOMP
Jul 12 08:34:45    mpd: ACFCOMP
Jul 12 08:34:45    mpd: [pt0] LCP: SendConfigReq #71
Jul 12 08:34:43    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:43    mpd: MP SHORTSEQ
Jul 12 08:34:43    mpd: MP MRRU 1600
Jul 12 08:34:43    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:43    mpd: MAGICNUM 9e646f84
Jul 12 08:34:43    mpd: MRU 1500
Jul 12 08:34:43    mpd: PROTOCOMP
Jul 12 08:34:43    mpd: ACFCOMP
Jul 12 08:34:43    mpd: [pt0] LCP: SendConfigReq #70
Jul 12 08:34:41    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:41    mpd: MP SHORTSEQ
Jul 12 08:34:41    mpd: MP MRRU 1600
Jul 12 08:34:41    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:41    mpd: MAGICNUM 9e646f84
Jul 12 08:34:41    mpd: MRU 1500
Jul 12 08:34:41    mpd: PROTOCOMP
Jul 12 08:34:41    mpd: ACFCOMP
Jul 12 08:34:41    mpd: [pt0] LCP: SendConfigReq #69
Jul 12 08:34:39    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:39    mpd: MP SHORTSEQ
Jul 12 08:34:39    mpd: MP MRRU 1600
Jul 12 08:34:39    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:39    mpd: MAGICNUM 9e646f84
Jul 12 08:34:39    mpd: MRU 1500
Jul 12 08:34:39    mpd: PROTOCOMP
Jul 12 08:34:39    mpd: ACFCOMP
Jul 12 08:34:39    mpd: [pt0] LCP: SendConfigReq #68
Jul 12 08:34:37    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:37    mpd: MP SHORTSEQ
Jul 12 08:34:37    mpd: MP MRRU 1600
Jul 12 08:34:37    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:37    mpd: MAGICNUM 9e646f84
Jul 12 08:34:37    mpd: MRU 1500
Jul 12 08:34:37    mpd: PROTOCOMP
Jul 12 08:34:37    mpd: ACFCOMP
Jul 12 08:34:37    mpd: [pt0] LCP: SendConfigReq #67
Jul 12 08:34:35    mpd: pptp0-0: ignoring SetLinkInfo
Jul 12 08:34:35    mpd: ENDPOINTDISC [802.1] 00 00 24 c8 6a 30
Jul 12 08:34:35    mpd: MP SHORTSEQ
Jul 12 08:34:35    mpd: MP MRRU 1600
Jul 12 08:34:35    mpd: AUTHPROTO CHAP MSOFTv2
Jul 12 08:34:35    mpd: MAGICNUM 9e646f84
Jul 12 08:34:35    mpd: MRU 1500
Jul 12 08:34:35    mpd: PROTOCOMP
Jul 12 08:34:35    mpd: ACFCOMP
Jul 12 08:34:35    mpd: [pt0] LCP: SendConfigReq #66
Jul 12 08:34:35    mpd: [pt0] LCP: phase shift DEAD --> ESTABLISH
Jul 12 08:34:35    mpd: [pt0] LCP: state change Starting --> Req-Sent
Jul 12 08:34:35    mpd: [pt0] LCP: Up event
Jul 12 08:34:35    mpd: [pt0] link: origination is remote
Jul 12 08:34:35    mpd: [pt0] link: UP event
Jul 12 08:34:35    mpd: [pt0] device is now in state UP
Jul 12 08:34:35    mpd: [pt0] device: UP event in state OPENING
Jul 12 08:34:35    mpd: [pt0] device is now in state OPENING
Jul 12 08:34:35    mpd: [pt0] attaching to peer's outgoing call
Jul 12 08:34:35    mpd: [pt0] device: OPEN event in state DOWN
Jul 12 08:34:35    mpd: [pt0] LCP: LayerStart
Jul 12 08:34:35    mpd: [pt0] LCP: state change Initial --> Starting
Jul 12 08:34:35    mpd: [pt0] LCP: Open event
Jul 12 08:34:35    mpd: [pt0] link: OPEN event
Jul 12 08:34:35    mpd: [pt0] opening link "pt0"...
Jul 12 08:34:35    mpd: [pt0] bundle: OPEN event in state CLOSED
Jul 12 08:34:35    mpd: [pt0] IPCP: Open event
Jul 12 08:34:35    mpd: [pt0] IPCP: LayerStart
Jul 12 08:34:35    mpd: [pt0] IPCP: state change Initial --> Starting
Jul 12 08:34:35    mpd: [pt0] IPCP: Open event
Jul 12 08:34:35    mpd: [pt0] IFACE: Open event
Jul 12 08:34:35    mpd: pptp0: attached to connection with xx.xx.xx.xx:52786
Jul 12 08:34:35    mpd: mpd: PPTP connection from xx.xx.xx.xx:52786