add existing item

hi,
when we make an asp.net application on a machine and take it to another system,it doesnot run or load.it set "the project is not set for debugging,either set teh debug=true in web.config". wat is this problem and hoe to over come it.how can we run an application made on ONE MACHINE TO BE ABLE TO RUN ANOTHER MACHINE IN ASP.NET,

ALSO,WAT R the files that we have to add in the project explorer window when we r adding an existing item through "add new item"(i klnow we have to add the forms,but what more r needed,i am a bit confused)

waiting for a response.
dotnet