The remote host is missing an update to pptpd announced via advisory DSA 1288-2.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201288-2

A regression in the handling of out-of-order sequence numbers of some MPPE implementations was fixed. For reference the original advisory below: It was discovered that the PoPToP Point to Point Tunneling Server contains a programming error, which allows the tear-down of a PPTP connection through a malformed GRE packet, resulting in denial of service. The oldstable distribution (sarge) is not affected by this problem. For the stable distribution (etch) this problem has been fixed in version 1.3.0-2etch2. For the unstable distribution (sid) this problem has been fixed in version 1.3.4-1. We recommend that you upgrade your pptpd packages.