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I'm trying to use a Linq datacontext from a partial trust environment (well, after Assert'ing my way back up) and I'm getting the spectacularly verbose error:-


Which looks like it's lacking an actual human-readable error but at least it's distinct!

In my case rather than asserting the individually needed parts I had to assert full-trust from my intermediary class (the one that is signed by a strongname to allow it to always be full-trust in my custom AppDomain - see my article on creating a restricted AppDomain - see one of the comments in the code example) between the untrusted plugins (things inside the appdomain with the restrictions applied can call into this and anything the intermediary class does is unrestricted but even things it calls get the inherited permissions from the caller) and the Linq data context user:-

PermissionSet set = new PermissionSet(PermissionState.Unrestricted); //fulltrust especially for Linq :(
//removed my carefully crafted assert set for Linq/SQLCE in exchange for the above being unrestricted:-
//set.AddPermission(new FileIOPermission(PermissionState.Unrestricted));
//set.AddPermission(new AspNetHostingPermission(AspNetHostingPermissionLevel.Unrestricted));

//Make the call to whatever uses the linq datacontext

Which was a little annoying, but worth knowing.  (The assertion will revert when the stack pops from the method this is in, however do be aware not to allow anything under this method to allow the plugin to execute a delegate or something).
I did find a possible workaround of moving a member variable I was accessing into a local variable in the Linq query, but this didn't work in my case where asserting this did.