When I start the CS, it gives a message that "Couldn't load plugin.esp, it doesn't exist". What does this mean? It seems to work OK. Is this supposed to be some sort of blank esp that one can use to create a new mod maybe. that brings up another question. How does one go about starting from a blank slate. In other words, just a fresh/blank esp that is not part of another mod.
Thanks

I'm not familiar with CS Extender or that error, but:

Making a new mod is just a matter of selecting to load only Oblivion.esm. Then you can make your changes/additions, and when you save it will ask what to name it.

If on the other hand you mean to make a total conversion (ie. whole new game), You'll want to find one of the http://www.tesnexus.com/downloads/file.php?id=3776 available.
This is only for a total conversion though.

Thanks! I can't believe it was that simple. Makes sense now.

The CSE allows you to define a default plugin that will load everytime you load the CS. If that's the error you're talking about, don't worry about it - it's not an error. You can into the CSE preferences and tell it you don't want a default plugin.

If you're just getting into modding, I suggest you go through some of the tutorials on the http://cs.elderscrolls.com/constwiki/index.php/Main_Page or http://tesalliance.org/forums/index.php?/forum/81-the-enclave/ first though - especially if you're running the CS with CSE. The ones on TESA are really good and a lot of fun to do actually!

Thanks for the info, I'm glad to hear that it's not an error. I'll check out the TES alliance link.