I looked back at some previous projects I have done with wireless comms. I have not used the Laipac modules, but have used the RFPICs and the Radiotronix modules.

I have used 1200 baud with one preamble, two start-of-transmission identifiers (STX), and one end-of-transmission (ETX) identifier. The packet data is between these wrappers. In my experience the manchester coding did not help much with short messages.

The only thing I was able to find was the following comments in my code:
Code:
/* for wireless link, the "invert" option should not be used
as this causes the transmitter to iddle on */
My point is, have you tried your code with T2400 (as opposed to N2400)?