Problem:- It is general problem that you are interested in generating the database diagram of a database and when you right click on database diagrams folder of database and try to create a new database diagram you get following error as shown in below snap.
The above snap says that you are not authorize person to generate database diagram so to resolve this we have to do following steps and then you are good to go to create database diagram
step 1:- Go to database properties by right clicking on database and choose files option from left side bar your will get following screen.
If you see above screen you will find the owner text box is empty.
Step 2:- Now click the button near by the textbox and you will get another popup window just select login “sa” user (or who has permission) as shown in below figure
Step 3:- Once it is selected the owner text box will be filled as shown in below figure now click on OK button
By following above 3 simple steps you will be able to create database diagram for particular database.
I hope this solution may help you if you stuck in such situation.
Thanks & Enjoy!!!