I just got done deploying a site to a GoDaddy hosted site only to find that one page where I had an ASP.NET Ajax UpdatePanel was throwing a MethodAccessException during the process of databinding to my object. After trying a bunch of things it turned out that I needed to switch my objects from internal to public. Normally you should be able to do reflection on a public member of an internal object in Medium Trust but GoDaddy must have unusual security settings for ASP.NET Ajax libraries.
This is an unfortunate thing to have to do but after messing around with this for an hour or so I'm just glad something will work. I'm not exactly sure why this is happening on GoDaddy because in my test environment I have <trust level="Medium" /> set so that I can debug issues like this as they come up but they must have some restricted settings on the ajax permissions.