blockUI produces unpredictable effects

blockUI produces unpredictable effects

I am developing a data driven website, since some data requests could take a long time so I use blockUI to alert users.  blockUI sometimes produces unpredictable results like the followings:
(1) The browser screen turns entirely black, the block message may or may not display.
(2) The overlay does not show up (this could be a result of opacity becomes 100%). The block message does display.

I suspect the problems are related to the amount of data and/or type of data returned by DB. I saved 2 rendered pages into:

The browsers having problems are IE6 and IE8 (FF3 works fine)  .
2.php shows black screen when "Get" button is clicked. 1.php appears to be working much better, but try to click on "Get" button continuously, sometimes black screen or blank overlay shows up.

I use jQuery version 1.3.2, blockUI  v2, I also use jQuery form for ajaxForm submission and jQuery Validate for form validation, but I don't believe ajaxForm or Validate will conflict with blockUI.

Thanks in Advance