I’m guessing that you are using this guide for the LimeSDR-USB https://wiki.myriadrf.org/LimeSDR-USB_Quick_Test
Do you by chance have a LimeSDR-Mini, which does not have onboard Memory that the LimeSDR-USB has which is required for that test to function.
There was an additional feature added to LimeSuite to generated a CW, but it also uses the onboard Memory on the LimeSDR-USB, so it will not work on the LimeSDR-Mini.
Maybe I’m wrong, but I what I think is being done, is that RAW samples are uploaded to the RAM on the LimeSDR-USB board, they are then continuously transmitted out a TX port (DAC) that is looped back around into a RX port (ADC) where the samples are received and displayed by LimeSuite. In my mind at least this could be modified to provide the samples continuously from RAM on the host computer. But maybe I’m overlooking something that is critical.