OK - found the solution here:
laatste bericht op pagina.
Before it got to work the PHP safe mode had to be turned off as well....
Thanks for pointing me in the right direction, I had looked before I posted, but not that far.
Please add these 2 things (even just for the time being) to the installation instructions, because I use a straight forward server and after having installed many software installations without a problem, one is very easily tempted to just give up and move on. It would be a shame to lose following over such simple things, because OpenGoo looks very, very promising!!!
Thank you developers for all your efforts.