During the last months I have been trying the should be easy experience of let watching 3D movies thru a 3D DLP projector. I haven't read any comments about that, neither the expert mags or blogs. The first main issue is that 3D bluray player must recognize a 3D device for playing the 3D contents. It's understood that all the devices (HDMI cables, switchers, etc.) are full 3D HD ready as well as the "order of switch on each one". Finally I was succesful with my Samsung BD-D8900 when I configured its "3D auto" feature that didn't let recognize the 3D device (the projector) to a "3D to 3D" one. That forced the player to send a 3D signal. I enjoyed 3D at last.  I looked afterwards for a better quality Bluray player and bought the high respected Sony  BDP-S790. To my surprise, the creators of the bluray technology were not able to make possible that this new device to send a 3D signal to my 3D projector. Again, Sony only had a "3D auto" feature and once more, didn't recognize as 3D my projector (a Mitsubishi HC7800D). Their only solution was to check everything and update software. I was obliged to return it back and continue with Samsung. I had looked for other manufacturers and no information in their manual instructions may assure that a different way of an "3D auto" configuration is possible and what happend when a real 3D device is not recognized when all the chain is full 3D HD. Do you have any experience or comments about that?  The best for this year.

As pointed out by Parsec all components of your infrastructure must support 3D.
This means especially the connecting cables. Older HDMI cables do not necessarily support 3D (version < 1.4). Version 1.3 (and lower) cables are still sold (usually in the bargain bins), so having bought the cable just recently doesn't really tell you which one you have. Some have the version imprinted on connector and/or cable others have this info only on the package.
Make sure to connect player and projector with 1.4 (or higher) cables and try again.

It sounds to me like a bad projector if you have to FORCE a 3D signal to it. To me, it says the projector is not communicating properly that it supports 3D.

Agree with Parsec and NewEnglander:
The projector is not communicating correctly with the player.
Since the cable is obviously capable of transmitting 3D content this leaves three possibilities:
1) Defective projector
2) Defective cable
3) Incorrect connection type

For finding out which one it is:
1. Connect the player directly to the projector with no other connections to player or projector

If it works as designed: one by one hook up all other connections until the error occurs again

2. Is the same as 1. but with a new HDMI connecting cable

If neither is bringing any improvement, I'm afraid that something inside the projector is broken.
If it's still under guarantee send it back to manufacturer for repair.