mmm.. excuse me.. but you are trying to read every checkbox using
checkboxi where i is part of the name of the checkbox??
First of all since this is asp.net the control will render to the page with the id that you give to it when you create it.
Second you can't reference a control that way since the compiler will think that the name of the control is checkboxi and will not know that that particular i should be a number since looks like part of the name.
the best aproach you have it's to do a findcontrol where you can do something like "checkbox" & i.tostring and it will resolve the control ok.
Read this if you want to know how to get a correct reply for your question:
^^Took that from dparsons signature and he Took that from planoie's profile