I was having the same problem using version 6.38.1 in both the client and the server. The client was getting stuck at "Link established"
In my case I have two routers, the server is a CCR1036 and the client is a RB2011UiAS. Fortunately for me we have two Internet service providers, one is BT and the other Virgin Media in the UK. The PPTP tunnel works fine over BT but not over the Virgin Media channel, then I realised that the Virgin Media CPE was filtering PPP traffic, as PPP pass-through was disabled in it's "firewall"
After disabling that filter the PPTP connection works fine over Virgin Media as well.
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