OK, something interesting....

I opened a new tab in MCSP and physically typed the following (shown as it appeared in MCSP):-

define OSC 8
include "modedefs.bas"

#CONFIG
__config _HS_OSC & _WDT_OFF & _BODEN_OFF & _PWRTE_OFF & _CP_OFF & _LVP_OFF
#endconfig

ADCON0 = $00
ADCON1 = $07
TRISB = %00000011
USBport var PortB.5

Once var bit
Once = 0

pause 1000

mainloop:
if once = 0 then
SEROUT USBport,T9600,["TEST",13,10]
once = 1
endif
goto mainloop

AND IT WORKED !!

I then modified the striped down file to be exactly the same as the above and IT DOES NOT WORK.
The "striped down" file was the original .PBP saved as another named file and then the bulk of the lines deleted.

It appears that it has something to do with the .PBP file created with the old version MCSP ???
This could explain why my recent use of Serout on the 16F88 worked as that code was created within the PBP3 version of MCSP.

I went back to old backups and tried those...same problem.
Could it be a corrupted .PBP file or some strange incompatibility between files created in the old version MCSP and the new PBP3 version ?

I'll post a question to Mecanique and see what they suggest.

Depending on what Mecanique come back with I will play around with recreating the 16F876A code, although, am not keen to retype 780-odd lines... will see how much I can paste.

This is a weird one !!