Hi Hixen and others,
Back just to let you know i found the answer to the permalink problem.
Turns out the plugin files of plugin WP4FB combined with Peerapong's great theme Jing were causing the problem. Even with the plugin itself deactivated, the files were still interfering. At least, removing the plugin files completely from the plugins folder solved the problem.
Of course i had tried deactivating all plugins, but the problem then persisted. Only after i decided to do a totally new installation of wordpress, the theme and the uploads and plugin folders, i found out that the plugins folder contained the solution. I then put all plugin in a tempporary folder and started putting them back in the plugins folder one by one. WP4FB finally turned out to be messing things up :).
Hooray and thanks for all the help!
Juuth