Error 0306 same here
A few things you might want to check (if you're willing to take your unit apart):
One possibility is a faulty door open/close knob on the front panel (this is probably a soft touch micro switch). Check for electrical continuity when pressed. If it needs to be replaced, you can use one from a scrapped CD/DVD-ROM unit, just make sure it's of the same type, otherwise you can get it on ebay or from manufacturers like Switchcraft, Piher, etc.)
If the unit has a belt driven mechanism for opening the cd door (also called the cd tray unit), see if the rubber belt is broken or has lost tension - in such case the drive motor is not able to open the door. If this is, in fact, the case, you'll need to replace the drive belt.
You need to find out its diameter, standard sizes can be found on ebay, just use the nearest standard size that is slightly smaller than your old drive belt (an old belt gets slightly oversized and that's exactly what causes it to loose its drag power).
Some mechanisms have a plastic wheel with a rubber edge which is driven by torsion from a motor - see if the rubber is greasy, damaged or dusty (you can clean it with some alcohol), but a replacement for these may be difficult to obtain since it's probably a brand/model specific part.
Then there are also mechanisms that are driven exclusively by gears (check gears for any broken teeth, also, the motor could be the problem). These are, again, brand and model specific parts and may be hard to get.
Another thing to check are the door open/closed switches. These are a pair of metallic contacts somewhat alike to a relay contact. They are usually located somewhere underneath the tray, possibly near the front end. See if the metallic contact points are dark with oxydation, if so, clean them by smearing them gently with a piece of fine sandpaper (be careful not to damage them, they may have a clear plastic cap-arm that needs to be removed prior to cleaning). There are usually two sets of such contacts in each tray unit, one for door open signal and one for door closed signal, so check both of them.
You can test the door motor by disconnecting it and running it of a 3 to 4,5 volt battery. If the mechanism is ok, the tray should open on one polarity and close when you reverse the battery poles (don't force it though, just run it for a few moments so that you see if it works fine).
From here on the things to check are motor connectors (any broken wires or bad solder contacts?), drive IC's, electrolytic condensers associated to the door motor drive section on the main circuit board.
So, there's quite a bunch of things that might cause the problem, also, could be that the true cause is something else.
Anyhow, i hope you can find out what the trouble really is and fix it.