I was getting a similar message for some time with my I-140. It said something like "This case number cannot be found". Funny thing is that before I got that message, I was able to get the proper message that said they had mailed a receipt and the case was in processing. After some time it corrected itself. It is likely only a problem with the automated system. Keep checking, and it will probably correct itself. You could try calling during the day and speaking with an agent, but I was never able to get through.
BTW, my RD is 3/14/02 and I'm still waiting. I-140 EB-1 EA. Anyone else waiting that long?