I've just upgraded to Umbraco 7.2.4 although it may not be related to this problem.

I added a couple of new users the other day and I just remembered I need to give them access to the Tea Commerce section.

I'm logged in as Admin and when I click a user's name in the 'Security' section I get the following error in TC 3.0.1

Server Error in '/' Application.

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Security Exception

Description: The application attempted to perform an operation not allowed by the security policy.  To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.

Exception Details: System.Security.SecurityException: Security error.

Source Error:

[No relevant source lines]

Source File: c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\a134b2ee\acb863ba\App_Web_edituserpermissions.aspx.6488e520.8itjfwgs.0.cs    Line: 0

Stack Trace:

[SecurityException: Security error.]
   TeaCommerce.Umbraco.Application.Views.Security.EditUserPermissions.OnInit(EventArgs e) +1072
   System.Web.UI.Control.InitRecursive(Control namingContainer) +186
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +12671271
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +12670781
   System.Web.UI.Page.ProcessRequest() +119
   System.Web.UI.Page.ProcessRequest(HttpContext context) +99
   ASP.app_plugins_teacommerce_views_security_edituserpermissions_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\a134b2ee\acb863ba\App_Web_edituserpermissions.aspx.6488e520.8itjfwgs.0.cs:0
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +913
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +165

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34237