Description
Because a blocking operation can allow the application to be re-entered (for example, by pressing a button while the operation is being performed), it is possible that another blocking function may be called while it is in progress. Since only one thread of execution may perform a blocking operation at any one time, an error would occur. The :IsBlocking Method can be used to determine if the client is already blocked, and if so, take some other action (such as warning the user that they must wait for the operation to complete). 

See Also
:Cancel()