I have had a major breakthrough in the past hour with what seemed to have been a problem with my server host 1und1.de in Germany.
When I first uploaded a 5.3 project to a domain at this host running PHP 5.2 over a month ago I was hugely frustrated that while the Search panel worked fine in the application-- the FORM that the users were to submit could not be submitted because it had one dropdown list field dependent on the dropdown list field value selected above it and both were Required!
This did not work. Select a top value and then the next field input was dead...no choices. Even though it had worked on my local testing server before upload to online.
TONIGHT, as I say, breakthrough!
It was my .htaccess file configuration that provided Mod rewrite for WordPress. The domain where I have moved my forms has no WordPress installed on it and I was running it in PHP 4.9 so that the dropdown dependency fields would work--- even though the Search panel would not. Lesser of two evils situation.
But, I have just upgraded this domain to PHP 5.2 and the dropdown dependencies WORKas does, it appears, the Search panel!
Glory!
I will have to experiment next on whether on a site where I have Wordpress installed that needs the Mod Rewrite can be disabled with a separate .htaccess file in the directory with a PHPRunner 5.3 project.
A BIG RELIEF that I have spent weeks bending Sergey's ear about!