Hey,

If you add a reference to an assembly in your project, if you look at the properties window for that reference, you will see that you have the option to copy that assembly to the output directory or not. This means that the assembly will either be copied to the debug/release folder or not. It might be the case that the assembly is already available on the server you are deploying to, i.e. in the GAC folder, so sometimes you don't need it copy it, but most times you do.

I think the difference stems from the reference that you have added. Check the properties of each.

Gary