Do they work together?

I have a couple of pages (say P1 and P2) in ASP.NET with C#. I have marked
bookmarks on both pages. On P1 if I click on a link it should go to bookmark_n
on page 2. So I put the link as (hyperlink control) "P2.aspx/#bookmark_n.
It goes there fine. No problems.

On that page P2 I have a login system with username and password. Only for
the first time when the user types username and password correctly, the page
works. If I type wrong password and try to test the page, then the code runs
fine to do what I want but the page is displayed in white space and all the
data on page is gone and it ignores everything including stylesheets etc.
BTW the usernames and passwords I store in an XML file on server. That is
not the question. If I remove bookmarks does this work OK? I have not tested
it yet but do the bookmarks and ASP.NET go hand in hand OK? Thanks for your
help in advance.