help with the Dell DataSafe usage model

I'm new to this forum so appologies if this is a covered topic.  A pointer would be appreciated.

OS: Vista Ultimate

Platform: Studio 1533

I've a couple of issues here that I need some help with.

I performed a backup of selected Document files a few weeks ago.  Today, I backed up a some pictures and discovered that my Document backup was superceded.  Is this expected?

A few more facts.

For the initial backup I used my default account however since then I've taken to the practice of using a non-priv'd user account and a priv'd admin account.  When I did 2nd backup, I had to do it from my priv'd account because DellDataSafe.exe would not run from my non-priv'd account even if I ran it "run as administrator" - the image would not run - no messages - no events in the event file - no nothing.  I found that it would run from my priv'd account.

I also am finding that I cannot backup my \Users\NonPrivd account from my priv'd account even when I "run as administrator"

So my questions are

What is the usage model of the software i.e. can I have files from multiple backup sessions or is there only one backup set stored?

Why can't I run DellDataSafe.exe from my non-priv'd account?

Why can't I backup my \Users\NonPrivd account from my Priv'd account.