I am trying to upload pdf files onto a site. It use to work and now I get a message similar to below

A critical error has occurred. Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.

I have tried to use File Manager but I get the following error message:

Error: File Manager is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed. ---> System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed. at System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet) at System.Security.CodeAccessPermission.Demand() at System.IO.DirectoryInfo.GetFiles(String searchPattern, SearchOption searchOption) at System.IO.DirectoryInfo.GetFiles() at DotNetNuke.Entities.Portals.PortalController.GetFolderSize(DirectoryInfo dirInfo) at DotNetNuke.Entities.Portals.PortalController.GetFolderSize(DirectoryInfo dirInfo) at DotNetNuke.Entities.Portals.PortalController.GetPortalSpaceUsed(Int32 PortalId) at DotNetNuke.Modules.Admin.FileSystem.FileManager.UpdateSpaceUsed() at DotNetNuke.Modules.Admin.FileSystem.FileManager.BindFileList() at DotNetNuke.Modules.Admin.FileSystem.FileManager.Page_Load(Object sender, EventArgs e) The action that failed was: Demand The type of the first permission that failed was: System.Security.Permissions.FileIOPermission The Zone of the assembly that failed was: MyComputer --- End of inner exception stack trace ---

Has anyone experienced this before or do you have any thoughts ?

any help would be greatly appreciated

regards

Tallisman