I have my application/website (Centre Of Excellence) running on server1(hstslc). Now I need to migrate it to another server(psicf). What I did was i took back up of Server1 and restored it in server 2. Now I made the following changes in the connection String & App setttings in webconfig file and executed.

Webconfig file

<connectionStrings>

<addname="SiteSqlServer"connectionString="Server=hstslc;Database=dbdb;uid=ipl;pwd=coepwd;"ProviderName="System.Data.SqlClient" />

</connectionStrings>

<appSettings>
  
    <add key="SiteSqlServer" value="Server=hstslc;Database=dbdb;uid=ipl;pwd=coepwd;"/>

    ... ... ... ... .. .. .. .... ...

</appSettings>

Changed to :

<connectionStrings>

<add name="SiteSqlServer" connectionString="Server=psicf;Database=coedb;uid=uid1;pwd=pwd1;" ProviderName = "System.Data.SqlClient" />
</connectionStrings>

<appSettings>
  
    <add key="SiteSqlServer" value="Server=psicf;Database=coedb;uid=uid1;pwd=pwd1;" />

    ... ... ... ... .. .. .. .... ...

</appSettings>

But It shows the following error. Any idea what else needs to be done ?

Server Error in '/CentreOfExcellence' Application.

Object reference not set to an instance of an object.

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.NullReferenceException: Object reference not set to an instance of an object.
 

If I change the connection string to the old one i.e., server1(hstslc), its working absolutely fine

What could be the problem ? Help Me !!