RFM70 works not relably

Hi,

there are some infos concerning RFM70 but I haven't found what I was 
looking for.

I have connected 2 RFM70 to 2 ATXMEGA 128 and it works pretty well and 
at reasonable distances (2 floors) but only when sender and receiver 
aren't moving. When I walk around with the receiver some data pakets are 
lost. My program always has the auto-ack-function enabled. Also I tried 
the auto-retransmission function. Then, after 15 tries of this function, 
I switched on the Re-Use mechanism (REUSE_TX_PL) with a timeout (without 
switching off auto retransmission). This didn't work either. Still some 
pakets are lost.

Sometimes, the receicer blocks and I can make it work again by a reset 
of the processor (but this is not my main problem)

For my final purpose I need very reliable data transfer and the receiver 
will move around.

Does anybody know whether successful auto-retransmission causes an 
interrupt? Thats not mentioned in the instructions.

Does anybody have a suggestion how to make these transmissions safer? 
Shall I flush the transmission buffer and start transmission again after 
15 tries of the auto-retransmission function? can it be a hardware 
problem (the parts are only plugged together but this seems to be OK).

Thanks for any suggestions!!