TaoNow,
Thanks for your reply.
I went to Chaeng Wattana this morning.
I did have a printout of the acknowledgement page of the last 90 day report (online).
But unfortunately for this immigration officer that was not good enough as the 90 day report was "too old" (about 1 year old, I have since traveled in/out of Thailand several times, so 90 day report was not needed).
So they told me to either wait 90 days, do a new report and then apply for the Residence Certificate, or get it from the embassy instead.