Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.

ref

http://forums.asp.net/t/1048637.aspx

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=147013&SiteID=1

http://aspadvice.com/blogs/joteke/archive/2008/08/24/Is-_2200_Databinding-methods-such-as-Eval_280029002C00_-XPath_280029002C00_-and-Bind_28002900_-can-only-be-used-in-the-context-of-a-databound-control_2E002200_-causing-you-grief_3F00_.aspx

http://bytes.com/forum/thread471988.html

http://www.codeproject.com/KB/aspnet/SheriefSayed.aspx?display=Print