I will be graduating with a Masters degree in December, 2010. I applied for my OPT in September. I just received an RFE on my OPT application. The RFE asks me to submit evidence (previous I-20) that shows the level of education achieved at the time I had been granted my previous OPT which was from Feb. 2009 to Feb. 2010. That was the OPT I had received after completing my Bachelors. I had sent them a photocopy of that EAD card with my current application, but had not sent the previous I-20 (from my Bachelors). Note that I did not complete that OPT, and began going to grad school in September, 2009 which effectively cancelled my first OPT.

I will be sending them a copy of the old I-20 (as requested on the RFE) and a copy of my Bachelors diploma. My question is, has anymore had a similar RFE? Is it a requirement to send old I-20s with your OPT application, if you have had an OPT in the past; a requirement that I and my school official had simply overlooked? Or is it something more serious? I guess I am kind of spooked that my OPT will be denied, especially since I already have a job offer that is set to begin as soon as I receive the EAD.

Let me know what your thoughts are?

This is obvious, since u didn't submit ur previous I-20s, they need to know why the previous OPT was granted for? They won't let u have two OPTs for same level study. At this time they know u applied for OPT with master level study. So they wanna know whether the previous OPT was for bachelor's level or for master's level. If the previous was for master's level then your OPT will be denied but as u said ur previous OPT was for bachelor's level, no worry it will be granted. 

In your OPT EAD application (I-765),section 11 clearly states you to check if you ever applied for a EAD and provide details and documentation of that application.