Openvpn unusual error

First off all I’m sorry for my bad English

I am installed mikrotik version 5.6 and done all of thing for ovpn server configurations.

Everything is done. But I have unusual error.
When I connect from my pc with openvpn to my server its work, I can search, download without problem, and after I checked openvpn is working, I send config files to my friends to check is it working?

Here is my problem:

server side:
16:50:55 ovpn,info : dialing…
16:51:55 ovpn,info : terminating… - could not negotiate TLS in time
16:51:55 ovpn,info : disconnected

client side:
Sun Oct 09 20:21:44 2011 TCPv4_CLIENT link local: [undef]
Sun Oct 09 20:21:44 2011 TCPv4_CLIENT link remote: 31.3.238.149:2106
Sun Oct 09 20:21:45 2011 TLS: Initial packet from 31.3.238.149:2106, sid=dcfe38ae cb38bcff

You might think hey that is firewall problem but it isn’t!
Here the reasons:

  1. One pc can’t connect to server (firewall is off)
    Above problem
    When connect pc to my modem, the pc connected successfully.
    I think maybe modem has problem then I decided to change modem but it’s not worked.
    I reset modem and set again pppoe and try to connect, bingo it’s connected.
    Yes modem has a problem
    But when I saw this problem in another pc I try to reset modem and connect to server but it’s not working.
    I think maybe I must change MTU but not worked.
    What is the problem​:double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark::double_exclamation_mark:
    Some people can connect but some people can’t connect

Finally:
A: maybe mikrotik has a problem with openvpn – 70%
B: maybe ISP has a problem – 10% - because some people have same ISP registration .for some work.
C: maybe some modem has problem – 2% - because I changed modem but still not worked.

Same here with 5.7. I have RB450G with OVPN enabled on port 443 and about 15 clients. Most of them can connect, but at least 3 cannot connect with TLS timeout. We have even tried Windows re-installation (all clients are Windows), but it doesn’t help. Errors are the same as ramin110.