While previewing a SQL Server Reporting Services (SSRS) report today a warning popped up in Business Intelligence Design Studio (BIDS) that access was denied to System.Security.Permissions.ReflectionPermission.
It turns out I had incorrectly written an expression like this:
=(BlahBlah).Value
What I really meant was:
=BlahBlah.Value
If you see this error you may have done something similar