You can't simply copy / paste your code from older projects into the new Visual Basic .Net and expect it to compile and run. The process is a bit more complex than that. To be noticed that you need to be careful at some aspects before you begin. In this matter, you first should check your old projects and remove any dead or duplicate code section, upgrade problematic syntax and controls, make sure that you don't have any undeclared variables in your code. After you did all this, make sure to use the wizard in order to convert the code from VB 6 to VB .Net.
I strongly suggest that you follow the steps provided above to make sure that you properly migrate your programs. Also, you can use the following guide that you can download from the official website.