Don,
Did you command strobe SRFOFF after STXCAL?
The STXCAL enables and calibrates the frequency synthesizer and goes from a RX/TX to a wait state where only the synthesizer is running. However if you decide to use the SRFOFF command afterwards, it not only disables the RX/TX, but also disables the frequency synthesizer.
Also did you add a delay after the SXOSCON command to wait for the crystal oscillator to stablize before enabling the frequency synthesizer?