Basically I call a page that does a very long op
But I need to display a progress bar
no frames

There is an old trick in html and asp

for a page that has a long operation
Response.buffering is disabled and
initially div with progress bar is displayed
when page finally fully loads (when op is completed)
onload function makes div invisible

but for web forms does not work it seems
untill page_load finishes nothing is displayed whatever
Response.bufferoutput is set to false