Hi,
Have you tried replacing #a with DEC a? Not that I'd know why it would matter but it's worth a try.

Another thing worth trying might be to first write your whole string to an array and then using that in SEROUT2 statement. Perhaps the character timing gets screwed when the PIC converts the value the ASCII or something.

Something like:
Code:
myString VAR BYTE[40]
ArrayWrite myString, ["X1, 23.4, 56.7, m/s, a=",#a,", ",DEC WScnts,10,13,0]  'Pad a zero at the end to terminate the string.
serout2 S_out, B12I, STR myString
I've not tested the above, shown for "illustration purposes" only ;-)

Well, not much help, just some ideas.

/Henrik.