Help needed installing Sage CRM 7.3 SQL Database connection error

Hello to everyone,

i am dealing with the following issue. I am trying to install Sage CRM 7.3 on our local server and i am faced up with the following error. When i am at the step where the user has to connect to the database he want to use or create i always receive the same error (pls see the picture).

At the beginning i installed sql server 2014. I had this issue and i though i will choose install sql express in order to see how it will go forward (of course i uninstalled the sql server 2014 installation before the installation of the express version). After the installation i have to follow again the same steps and the error is still there. i read the sage installation guide and there is written that if we use the sql express edition we can login with the following access data:

Username: SageCRM73
Pass: crmsqlexpress

i checked the port etc and seems to be right. Can someone provide me a detailed guide or something similar. Or just tell me about his/her own experience?
Thank you in advance.