objects sometimes recognized and sometimes not

I am running QTP which opens a browser that has a place to enter login and password (similar to the flight demo). I added the boxes to the repository and put them into my QTP script (enter text in theusername box, enter text in the password box, and click login).

Sometimes when I run it it works fine.
Other times when I run it it says it can't find the objects (in runtime).
This happens with other objects to. A popup window somes up and
I can click buttons on it one time, and the next time the objects aren't
recognized.

In the case with the login, I don't know what is going on. Object spy seems to identify the objects, and the web site has not changed.

For the popup window one thing I noticed is sometimes an object is
called browser("xALIWeb").page("report") and then other times it might be called browser("xALIWeb").page("report_2") or even
browser("xALIWeb_2").page("report")

Why would boject names change like this? And what is happening with the login? It is only one page.