Debian Squeeze 6 is absolutely not the best choice in these days as it's a quite old version of Debian, which is not officially supported and maintained by the Debian project itself anymore - just from a small group of people and companies till February 2016. The delivered software packages are also not really the latest ones. As Xuxe said, this old packages maybe causes your issues. So please install the latest Debian 8 on your server and try it again.