Welcome to FixYa.
I just would like to clarify what you posted. Are you certain it is "E2" and perhaps not "F2" ?
The "F2" on the SC302 wall ovens indicates an overtemp was detected by the onboard watchdog in the control board.
( The lock indicator being on is simply a byproduct of the unit being in self-clean at the time the error occured ).
What this means can actually come down to a couple of things, either an intermittent temp sensor or ultimately a bad main relay board.
In the SC302 service manual I have instructs simply to replace the temp sensor. If the F2 reappears replace the main relay board...but not so fast.
* The one exception which is not mentioned in the manual but I have experienced first hand in the field is this...A tripped overtemp safrety cut-out.
Here`s what to look for for this,
Fortunately if it is tripped, they are the manual reset type and are accessible
behind the black grill/vent just above the door and just below the control panel next to the lock latch assembly.
**Turn off the 40amp breaker at your service panel or sub-panel in the home before attempting any service...safety first**
With the power off, you should be able to remove the grill and push the red button in the center of the thermostat and that should fix your problem...if indeed the hi-limit is tripped you`ll know immediately because you`ll feel it click as you push it down. It will look like the image below...
If you feel capable of repairing this yourself I can send you a complete service manual in a "pdf" attachment, however you`d need to provide an email address to where I could send it to you.
Other than that if you call in a pro just be sure they are an authorized B/S/H/ service provider ( B/S/H/ is the parent company for Bosch, Thermador, Gaggenau, Siemens products ).
Let me know and I`ll watch for your reply and respond as soon as I can.