Add a new user using csharp

Hello

I'm using a data base Access and I want to Add or to edit a user, I  click on "User" and  I write the informations (in the "New User" form or in the "Modify user" form) then I click on confirm but I get allways the same error "System error",please can you help me tell me where is the error in my code ????
Thank you in advance 
Good day

PS:Amember of the Csharpcorner helped me to develop the attached code and I'm really thankful for him.