Please check whether your config file looks like this.
-->
<configuration>
<appSettings />
<connectionStrings>
<add name="MainConnStr" connectionString="server=localhost;database=myDb;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
</connectionStrings>
<system.web>
</system.web>
</configuration>
updated:
it looks like you have .net framework 1.1 and 2.0 application hosted together.
Check this.
http://forums.asp.net/t/1080128.aspx[
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