Use Ms Access mdb instead of SQL mdf as login db

I build a simple ASP.Net Web Form site with login using VS2017 template.

Now it is ok and is using SQL mdf.

I follow some advices on web to change to use Access mdb instead.

I already generated Access Provider dll file and copied that to Project Bin folder, and I have copied the mdb file to App_Data.

Then I modify web.config accordingly.

However, when run on VS2017 Development server and enter user name pwd and click Register, it goes to error re

IdentityModels.cs in the line

public ApplicationDbContext()
            : base("AccessFileName")

Error is System.ArgumentException: 'Format of the initialization string does not conform to specification starting at index 0.'

What happened ? Please help. Thanks