Partner SFB/FB is in the wrong state.

The receive block was not called again after the last data transmission.

In other words, you try to send again before the data was completely received.
In my opinion, the cycle time of the receiver is slower than that of the sender.
Or you do not interlock the send job correctly (waitingfor the done bit before retriggering a new send.

Have a look to the FAQ:
http://support.automation.siemens.com/WW/view/en/18516182