Recently, we were using Custom workflow activity in which we were calling report server(using IP address) web service for generating SSRS report. We were using this custom WF activity in one workflow as a step which was getting triggered on create of a record.
While testing this functionality, we got the below error message and the workflow was failing: “System.Net.WebPermission, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 failed”
To fix this error, we deployed the custom workflow activity assembly using non-sandbox mode as shown below:
Hope it helps !!
Ajit Patra 