I have changed my code to:

 btPhoto.OnClientClick = "javascript:showpic('imPhoto','" + fl.Substring(fl.IndexOf("photos\")) + "');"

And I have added this function to the aspx page:

<script type="text/javascript">
    function showpic(objID, objSrc) {
      var bigpic = document.getElementById(objID);
      bigpic.src = objSrc;

      return false;
    }
  </script>

The function is called, that I checked by replacing the first two lines with an alert.
But the above code is not working. The page, when shown in IE, gives errors, but they don't say anything usefull.

Any solutions?

rg,
Eric