Dave, it's the same thing as from post #6.

If there is an HSERIN or HSEROUT anywhere in your program. PBP will initialize the USART at the beginning of the program, before jumping to user code.

If you don't set the defines, PBP defaults to 2400 baud and standard USART mode (8-bit BRG).
Anything above 32mhz, and 2400 baud is too slow for a standard USART. SPBRG ends up larger than 255, and throws an out of range warning.

If you define HSER_SPBRG, then PBP does not try to calculate SPBRG ... hence no warning.
If you define an HSER_BAUD that works at that OSC, it calculates a valid SPBRG and also doesn't give a warning.

Once you've made it past the Initialization, you can manually set the EUSART registers for whatever baud rate you want.

hth,