CAS Permissions

I have a simple window form application. It runs fine when the executable is
saved on a the harddisk. I uploaded the executable on my website and then
used internet explorer to download it; at the prompt I chose "run" instead
of "save" and the executable threw System.Security.Securityexception. I know
this has to do with CAS permissions. How can I fix this? Optimally I'd like
a solution that autimatically grants my executable Fulltrust whenever (and
wherever) its run.