I made a mistake by changing something I should not.
My system is dutch so I must translate, which is probably not always clear, sorry for that.
Here is what happened:
I opened filebrowser and I saw a little icon with two heads under my external hard drive. I thought that has something to do with sharing. I right clicked on this external hard drive and chose 'sharing with'.
Then on 'advanced sharing' and a new window opened.
I choose the label 'security' and there I saw three user groups to have acces to my hard drive. The first was EVERYBODY (or everyone) which surprised me so I changed it. Now I do not have acces to my harddrive at all and I can not change it back either. It says 'you should have reading permission to see the properties of this object', (or so).
Can anybody guide me through the process to reverse my misstake?
looking for a sollution I found out that I never enabled the possibillity to restore the last systemchange. Well they say one learns from ones mistakes.