App crashes when I try to read QString from socket - qt

Question

I am trying to develop a Qt program using sockets for client and server communication. I need help with figuring out why my server crashes when the client connects and the server tries to get a QString?
I have this code on the server side:
void Client::onReadyRead() {
qDebug() << "On ready read!";
QDataStream in(mSocket);
in.setVersion(QDataStream::Qt_4_0);
for (;;) {
if(!mBlockSize) {
if (mSocket->bytesAvailable() < sizeof(quint16)) break;
in >> mBlockSize;
}
if(mSocket->bytesAvailable() < mBlockSize) break;
qDebug() << "Package was recieved!";
qDebug() << "Block size: " << mBlockSize;
if(Table::INVALID_ID == mUser.id()) {
QString authStr;
in >> authStr;
qDebug() << "Recieved account data: " << authStr;
}
mBlockSize = 0;
}
}
And on the client side:
void Client::onConnected()
{
qDebug() << "Connected!";
QByteArray block;
QDataStream out(&block, QIODevice::WriteOnly);
//Reserve 2 bytes
out << (quint16)0 << mEmail << "|" << mPassword;
//Back to the beginning
out.device()->seek(0);
//Write a block size
out << (quint16)(block.size() - sizeof(quint16));
mSocket->write(block);
}