When overridden in a derived class, ends an asynchronous append operation.
A reference to the outstanding asynchronous I/O request.
One or more of the arguments is invalid.
The method was called after the sequence has been disposed of.
This method blocks until the I/O operation has completed. Errors that occur during an asynchronous write request, such as a disk failure during the I/O request, become visible when EndAppend is called.
This method must be called exactly once on every IAsyncResult returned by the BeginAppend method.