Solved.

I assumed that Reading and ACKnowledging was enough to cause the MSSP
to do another read.  It turns out that a initiate read ie setting RCEN
is required for every read, not just at the start of the random read.
It seems obvious now but it did not appear so obvious when reading the
manuals and App Notes.

So I originally had

	banksel SSPCON2 ; select SFR bank
	bsf SSPCON2,RCEN ; initiate I2C read
		; This code checks for completion of I2C
		; read event
	btfsc SSPCON2,RCEN ; test read ********************* I sthis right
		; bit state
	goto $-1 ; module bus  so wait

read_next_byte:                              ;If code runs to here ok then =
first
byte appears to be read ok
        banksel         SSPBUF
        movfw           SSPBUF        ;read the byte
        banksel             SSPCON2       ; select SFR  bank
        bcf                    SSPCON2, ACKDT             ; set ack
bit; state to 0
        bsf                    SSPCON2, ACKEN             ; initiate ack

                                                        ;the following
lines are included for debug only
        banksel         PORTD           ;display value for debug
        movwf           PORTD
        goto               read_next_byte:

changed to this code and now it works.  This includes the RCEN setting
for each read (and re-arranges the order of the ACK - Read steps but I
am not sure if that makes any difference.)

read_next_byte:                              ;If code runs to here ok then =
first
	banksel SSPCON2 ; select SFR bank
	bsf SSPCON2,RCEN ; initiate I2C read
		; This code checks for completion of I2C
		; read event
	btfsc SSPCON2,RCEN ; test read ********************* I sthis right
		; bit state
	goto $-1 ; module bus  so wait


byte appears to be read ok
        banksel             SSPCON2       ; select SFR  bank
        bcf                    SSPCON2, ACKDT             ; set ack
bit; state to 0
        bsf                    SSPCON2, ACKEN             ; initiate ack

        banksel         SSPBUF
        movfw           SSPBUF        ;read the byte


                                                        ;the following
lines are included for debug only
        banksel         PORTD           ;display value for debug
        movwf           PORTD
        goto               read_next_byte:
--=20
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