🚀 go-pugleaf

When viewing a .pdf file, I usually prefer to use the up and down arrow keys and the Page Up and Page Down keys to navigate through the document.  Sometimes, however, for no *apparent* reason, these keys will cease to work at all, and I have to resort to using the scroll bar or the Next Page/Previous Page buttons.  Also, when the arrow keys *do* work, sometimes they allow continuous scrolling (i.e. holding the key down) and at other times I have to keep pressing the key over and over again to move up or down.  Can anyone explain this?  Am I simply stupid, or am I doing something wrong and not realizing it? 

Specifics: This happens while using Acrobat 4.0 via Internet Explorer 5.00 (i.e. using my Web browser to view a .pdf file on the Web); Windows NT 4.0; Compaq Presario, Pentium III 500 mHz. 

This seems like such a simple issue, but I can't find any pattern to suggest why it behaves in this way.  Sometimes it works, sometimes it doesn't.  Any answers or constructive criticism welcome.