MSSQL Error 'The underlying provider failed on Open'

Question

I was using an .mdf for connecting to a database and entityClient. Now I want to change the connection string so that there will be no

Answer 1

I had this problem because the Application Pool login this app was running under had changed.

In IIS:

• Find the Application pool by clicking on your site and going to Basic Settings.

• Go to Application Pools.

• Click on your site's application pool.

• Click on Advanced Settings.

• In Identity, enter account login and password.

• Restart your site and try again.