The PDF and Excel rendering extensions require UnmanagedCode permission to operate at all times.
You can check out the Medium Trust Support
article to find out more about the limitations and requirements for deploying an ASP.NET application containing Telerik Reporting on a web host that imposes Medium Trust permission level.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.