URGENT help needed. Server Error in '/' Application.

I need some major help here. My asp.net website was working fine until about an hour ago. Now whenever I try to login I recieve this error;
 
Server Error in '/' Application. Configuration Error Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level.  This error can be caused by a virtual directory not being configured as an application in IIS.

Source Error:


Line 48: <allow roles="Administrator"/> Line 4 ...