I have done all the things specified in the Link.
While analysing the /var/adm/messages file I noticed an error occuring. I have done some researches and found the following link with someone having exact the same error.
It seems that the actual Patch Level which is installed has a bug that does not allow to access the system as a non-root user.
I will install an actual patch and will post the results.
Thank you so far for your help!