What is 'Error BC30456? (Not a member of ASP.Default_aspx?)

[Guest]

I've followed the rules. I'm trying to implement an edit linkbutton on a
datalist, but whenever I try to compile, I get the above error. The sub is
there, with the correct name, the itemtemplate is correct...etc. Everything
is in the correct format, and all the names are spelled correctly, yet I keep
getting that error. What is it? and, What causes it? How does one go about
getting rid of it?

Thanks in advance