Please help

Ok, this problem is becoming pretty annoying. I've tried many ways to do this, but can not find a way that works, and I can not find out why I am getting this error. The line the error is triggering on is:

document.getElementById("resultsframe").src = "searchresults.aspx"

It says:

Compiler Error Message: BC30451: Name 'document' is not declared.

How in the world is document not declared? What did I do to mess it up? Any ideas?
Thanks.Are you trying to run client-side script from server?
Cause line of code you type is client-side javascript, but exception you get is server-side exception.