Upgrading COM+ to C# code

We have an application which was written using COM+ objects(.NET v1.1) and right now we want it to be upgraded to C# code(.NET v3.5). Please tell what all difficulties i will be facing?

The only thing I can get out of your question is that you wrote some code in .NET 1.1 and used COM+ to deploy these middle tier objects.

If that is true you are already .NET. Great. When you use COM+ services in .NET, this is called Enterprise Services. I only say that because it makes it easier to Google (example: http://msdn.microsoft.com/en-us/library/ms952392.aspx).

Is what you are asking: "When we move to .NET 3.5 and VS 2008 (or maybe VS 2010), what would be using?"

You might be able to keep using what you are using and just recompile. However, there is a semi-soft line between .NET 2.0 and what came before. I tend to find quite a bit of obsoleted APIs or breaking changes, but not enough to kill your project.

You might write Windows Communication Foundation services instead? You could probably break out the logic of your .NET 1.1 code into WCF services.

Again, it is pretty unclear what the specific challenges you are facing. Hopefully you can google Enterprise Services and WCF and perhaps read some Getting Started documentation. It may be what you are looking to transition to.