General migration issues - .NET 1.1 to .NET 3.5 [Part - 1]

1. New method "GetObjectData" is added to DataSet class: Since we were using this name for our custom Dataset, we had to overload this method.
Check This out.

2. Warning as Error: 'System.Xml.Xsl.XslTransform' is obsolete: 'This class has been deprecated. Please use System.Xml.Xsl.XslCompiledTransform instead.

XSLTransform calss is depricated and better performing XslCompiledTransform is inroduced.
Check this out for Migrating From the XslTransform Class.

3. Warning as Error: 'System.Xml.Schema.XmlSchemaCollection' is obsolete: 'Use System.Xml.Schema.XmlSchemaSet for schema compilation and validation.

XmlSchemaCollection calss is depricated and better performing XmlSchemaSet is inroduced.

To traverse through XmlSchemaSet we should use XmlSchemaSet.Schemas() method.
foreach (XmlSchema schema in schemaSetObject.Schemas())
{
      xmlSchemaObject = schema;
      .....
      ....
}
4. Warning as Error: 'System.Configuration.ConfigurationSettings.GetConfig(string)' is obsolete: 'This method is obsolete, it has been replaced by System.Configuration! System.Configuration.ConfigurationManager.GetSection'
Visit this link if you need more info on how to use GetSection Method. 

5. Warning as Error: 'System.Runtime.Remoting.Channels.ChannelServices.RegisterChannel(System.Runtime.Remoting.Channels.IChannel)' is obsolete: 'Use System.Runtime.Remoting.ChannelServices.RegisterChannel(IChannel chnl, bool ensureSecurity) instead.'

More info here.