QLocalSocketPrivate::completeAsyncRead:connection error

What does following error means (as got thru errorString()) ? I could not find anything about it in Qt Assistant (Qt 4.7.3)

QLocalSocketPrivate::completeAsyncRead:connection error

I am using QLocalSocket and QLocalServer classes for 'file transfer' from client to server basically similar to IPC fortune example. For the same file transfer example i have implemented thru QTcpSocket/QtcpServer and theres no error. Why this error comming when using QLocalSocket and QServer classes.