for creating own exception class,you have to derive your class
from System.Exception class.also you have to implement all
constructors which base class implements.to create own
exception class follow the requirements/recommendations
below-

to convert bitmap image file to gif file you
have to create bitmap object first.

there are many starter kits for visual web
developer to learn asp.net 2 and do the
common scenarios of web development.

if you have a asp.net web page which is derived
from a master page then you may have trouble
using a form inside your page.It happens because
of your master page using a form.It's a little tricky
to be able to use another form which you need to use.
you have to use a javascript line for that.

the following codes uses FileUpload control to
upload file to server.it's a example for
uploading files to the server using asp.net
and c#.