The error you encounter is a general one and could occur as a result of different reasons.
However, I have replicated such an error when the connection string declaration is missing in the web.config file.
I have prepared a runnable sample project for you to help you setup your project. It is attached to this message.
For this sample, the connection string declaration in the web.config is as follows:
<add name="NorthwindConnectionString" connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|Northwind.mdf;Integrated Security=True;User Instance=True" providerName="System.Data.SqlClient"/>
You may need to add a similar line in your web.config. Note that you need to change the "Data Source=.\SQLEXPRESS" instance with the one of your SQL server instance, in order to run the sample. In your case, it may be something like "Kevin\SQLEXPRESS".
About your second question on how to get at the value, I am not sure if you need it on client-side or server-side. I am sending you a Client-side Programming article
from the RadSearchBox Documentation. You can find Server-side Programming documentation there, as well.
In addition, I am sending you the Client-Side Events
and the Server-side Events
I hope that would solve your issues.
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