If your hosting service is running in medium trust environment, could you please set your local installation to medium trust (in web.config).You can follow the instructions in the User Manual to get it working locally in medium trust.
1. On your local installation open web.config and in system.web section add this line:
<trust level="Medium" />
This will insure that the website is running in medium trust, regardless is it on your local machine or remote server.
2. Open the Sitefinity User Manual and follow the instructions on page 254, section name "Medium Trust Support".
: possible reason for this error could be when you are trying to run Sitefinity on a 64-bit platform attempts to load a DLL that does not support native 64-bit execution. If the application. Is your production based on 64 bit OS? To fix this, the application should run in 32-bit mode and allowing the 32-bit dll to be accessed.
the Telerik team
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