moving ASP.net site to new 2016 server breaks connection string to SQL Server

Hi,

I maintain an ASP.net site for a friend on a hosting company's server.  They recently either upgraded the server to Windows 2016 or moved it to a 2016 server.  Now it throws the error when going to a page that access the SQL Server database:


Server Error in '/site1' Application.

The ConnectionString property has not been initialized.
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

 Exception Details: System.InvalidOperationException: The ConnectionString property has not been initialized.

Source Error:
 An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace:

[InvalidOperationException: The ConnectionString property has not been initialized.]
   System.Data.SqlClient.SqlConnection.PermissionDemand() +7022674
   System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection) +30
   System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions) +318
   System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +132
   System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +246
   System.Data.SqlClient.SqlConnection.Open() +122
   Timb.usedEquipment.BuildCategoryMenuDT() in G:\Files\860664\Timb\usedEquipment.aspx.cs:68
   Timb.usedEquipment.Page_Load(Object sender, EventArgs e) in G:\Files\860664\Timb\usedEquipment.aspx.cs:42
   System.Web.UI.Control.OnLoad(EventArgs e) +109
   System.Web.UI.Control.LoadRecursive() +68
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1436
 
I know very little about .net sites; all I've done to date is make minor static content changes.  The last change of any type was in early January, and to the site logic, several years.

The hosting company is saying it is an issue within the site.  While that may be true, it was working before the move and doesn't now.

Should I punt this back to them or try to figure out what the actual root cause is?  I wouldn't even know where to start.  I don't code in .net.

Thanks!

--Ben