In visual studio MyProject properties I set the Login.aspx page as startup page and it works fine when I use the local host, however when I publish to the external host server the startup page is ignored and the aspx page in the URL is displayed. What am i doing wrong? host server has IIS6, 3.5 FrameWork

Startup Action, and specific page in this case is only used for Debugging purposes, not for the initial page to load on your web host.
If your web host is using IIS7, you can use the
<defaultDocument>web.config element.Otherwise, you can set the value in IIS (see here), or possibly find a workaround elsewhere.