Getting disconnected from OpenVPN server each hour

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http://serverfault.com – I am having a rather strange issue with my OpenVPN configuration. I am connecting from Windows 7 with official latest OpenVPN client to my OpenVPN server (OpenVPN 2.1.4 i386-redhat-linux-gnu). The problem is I am getting disconnected from my OpenVPN server exactly after 1 hour and I can't understand what directive/option is reponsible for this. Maybe it's a client issue? I have tried different Windows systems and Windows VPN clients. The Linux clients are working as expected with no disconnections. Could you please help me to troublshoot this issue? I have tried reading books and googling an (HowTos)