SQL Database Read Only

[Djiber]

Mine C# WinForm Application is using SQL Server 2008 Express and it's database to store/browse Data.

On computer which I've used to develop application everything is working, but on my brother's computer I get an Exception that Database is Read Only when I try to submit some changes.

I've menage to get it working with Connection string:

Data Source=.\SQLEXPRESS;AttachDbFilename=C:\MyApp\Base.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True

and with it, it's working.

But I would like to connect and use Database from my computer also so he should use:

Data Source=.\SQLEXPRESS;AttachDbFilename=C:\MyApp\Base.mdf;UID=sa;PWD=*****;Connect Timeout=30;Integrated Security=False;User Instance=False

so I can use same Server Instance at the same time from my computer:

Data Source=Bros\SQLEXPRESS;AttachDbFilename=C:\MyApp\Base.mdf;UID=sa;PWD=*****;Connect Timeout=30;Integrated Security=False;User Instance=False

As I'm aware 'sa' User by Default should have All Permissions.

Could someone Please explain me what I'm doing wrong?