Daughterboard xcvr2450 tx/rx

Hi everybody,
I’m new in GNURadio and USRP’s world. I’m working with ubuntu 8.04,
USRP2, daughterboard xcvr2450, and last trunk of GNURadio. I’m trying
(with GRC) to transmit and receive on the same USRP2 a sinusoidal
signal. (with frequency 50 kHz). In my trasmition chain at first I
generate a sinusoid with “signal source” block, after I transmit with
“usrp2 sink” block, and in reception chain I receive with “usrp2 source”
block and I see all with “fft sink” block. My program works correctly
only if I set the frequency to 2.4GHz. If I try to shift the frequency
to, for example, 2.45 GHz (or any other frequency) my program don’t work
correcly. What could be the problems, or What am I doing wrong? Which is
the tx / rx switching rate for this daughterboard?

Thank you in advance