Given the kernel you're using this could be (related to) this bug:
https://launchpad.net/distros/ubuntu/+source/linux-source-2.6.15/+bug/36014
Given the kernel you're using this could be (related to)
this bug:
https:/ /launchpad. net/distros/ ubuntu/ +source/ linux-source- 2.6.15/ +bug/36014