Tx_waveforms.cpp underrun problem

dear all,

i am suffering an under run error when running the tx_waveforms.cpp
example i tried it on the BASIC and WBX daughter boards and i tried
several combinations (i.e. amplitude ,frequency ,SPB ,wave frequency ,
wave form) but nothing works i am using USRP1 if any body has a certain
combination that worked with a certain daughter board i would appreciate
his help