OK. I think you were right on the DB connection string. Now, I'm getting this error:
An error occurred while getting provider information from the database. This can be caused by Entity Framework using an incorrect connection string. Check the inner exceptions for details and ensure that the connection string is correct.
Where does your asp.net application run - on the same machine? If not, configure the SQL Server to accept connections from other machines.
And what about the account the IIS is running with? Does that account have sufficient access rights to the database? I suggest SQL Server authentication instead of WIndows authentication - do not forget to configure your SQL Server to allow that.
What the f...? You are right, I tested it.
Look at day number 0: with SQL Server, it is Jan 1, 1900; with Excel: Jan 0, 1900.
The next bug is the leap year: Excel treats 1900 as a leap year (that's wrong!), while SQL Server correctly knows that 1900 is not a leap year.
In sum, those differences account for the 2 days difference in current dates.