USRP & BasicTx max freq?

I am a newbie to the radio. I am trying to find my way around and have
gone thru some of the examples.

I am trying to transmit (for right now) 2 tones from the BasicTx
daughterboard. My goal is to have a centerfreq of 150MHz. Basically I
have a test program that is modified from the
/usrp/host/apps/ file.

I am not looking to run with Python, but C++, so that is why I started
here. I am reading the 2 tone data from file and putting it into a
buffer. I output the data after opening the USRP with the call:
ret = utx->write (buf, sizeof (buf), &underrun);

I have 2 tones offset from a center frequency, which is set with the
utx->set_tx_freq (0, center_freq);

I have it working and verified with a SpecAnalyzer for up to 44.0 MHz.
If I get over that, it barks at me for having to high of a center

I thought the BasicTx was good up to 250MHz?

I can trace thru the “driver” code in and see that
there is a check for that 44.0 MHz limit.

Is this a Tx limit? and the Rx limit is 250MHz? Or am I missing