Hi Guys, [SOLVED, it´s a do-it-yourself-job] I have done some more reading
and found an issue where JAN explains this is an 1.7 feature conflicting with 1.66. 
So there are two options: Use Phoca Download 2.0.1 if you must or Migrate to Joomla 1.7 (preferred). Since I don´t want to migrate for now I installed Download 2.0.1 Which is working 
And I have read the instructions, changed .htaccess, and set Joomla to report at maximum
But I still can´t figure it out what is going wrong.
The message looks very clear: JHtml batch is not supported File not found.
If needed I can supply the full Call stack back and forward, Profileinformation, SQL´s etc
There is only one error in a language file /var/www/vhosts/balansgroep.nl/httpdocs/administrator/language/nl-NL/nl-NL.com_phocadownload.ini : fout(en) op regel(s) 551, but I don´t expect this will cause an 500
Maybe it is worth mentioning, but on the Phoca controlpanel not all the icons are translated (Tags and Layout are not)
And Yes I have installed Phoca Download several times. (not always succesfull
)Joomla 1.6.6
Server Apache provider-hosted
How can I make Phoca Download working?
Best regards, Foleor
