WSASocket() failed: 10013 when testing GRE

[guest]

Q: I have a client attempting to connect to a Microsoft RRAS server via PPTP.
The router is supposed to support GRE and PPTP passthrough.

I am using PPTPSRV and PPTPCLNT to test GRE traffic.

When I run PPTPCLNT on the Vista machine I get a successful connection via
PPTP but GRE fails with error:

WSASocket() failed: 10013

I've tried to look up this exact error but can't find it. What does this
man and how do I troubleshoot?

A: I suspect that GRP protocol is disabled by firewall or router.

1. Check the external router to ensure they have TCP 1723 and GRE protocol
enabled.

2. Disable firewall on your Vista client if there is any:
1) Stop Windows Firewall service, and uninstall 3rd party firewall
application.
2) Re-connect VPN.
What's the result?

If the issue disappears, the root cause should be faulty firewall setting
on client. If the issue is still there, perform CLEAN BOOT and setup VPN
again.

3. Clean boot & setup VPN again:
<How to implement clean boot?>
Let's disable all startup items and third party services when booting.
1) Click "Start", go to "Run", and type "msconfig" (without the quotation
marks) in the open box to start the System Configuration Utility.
2) Click the "Services" tab, check the "Hide All Microsoft Services" box
and click "Disable All" (if it is not gray).
3) Click the "Startup" tab, click "Disable All" and click "OK".
4) Click "OK" to restart your computer to Selective Startup environment.
5) When the "System Configuration Utility" window appears, please check the
"Don't show this message or launch the System Configuration Utility when
Windows starts" box and click OK.
6) Check whether or not the issue still appears in this environment.
Note: Temporarily disabling the Startup Group only prevents the startup
programs from loading at startup. This shouldn't affect the system or other
programs. We may still manually run these programs later.

And then, ensure no local firewall is running, and setup VPN again. Can
this resolve the issue?