Carl, 

Any chance you are running in 720p?  I have had issues in the past where if I reneter an M/E onto a keyer in another M/E for instance  ( such as rentering the clean of PGM on M/E 1 keyer) ...I can't take an M/E  to air....take this M/E off the keyer and no problem. 

Or...Reentering M/E's into DME's.... Built a double box effect where I had to fly a video in a box, and an associated FM frame. ( 2 boxes, 2 frames)  Stack 4 DME's on one keyer...two DME's got the same FM channels. ( fill/key pair), two DME's got a M/E 3 Main and Sub clean respectively.  once I enabled the 4th DME in the stack...I can't take an M/E to air. Disabile the 4th DME...no problem

Want to say I have also seen it where I can't take CCR to air but can't be 100% sure.

 I am told this is a "bandwidth" restriction w/ 720p.. Not sure if you would see the same thing if you run 1080i.  From the testing someone else did for me, it wasn't an issue in 1080i..but I can't say 100% it wouldn't be...just wasn't for the example my friend was trying for me. 

I would check all your keys...make sure you don't have any M/E's on them...I know you mentioned CCR, but since M/E's are internally generated sources also,  you might be having  the same sort of issues I have.  Also, un-assign DME channels.  Then build your "layers" one by one and see where you are getting stuck. If you have CCR in pst, be sure to switch away and back since it will hold if already there...but you won't be able to get back.  This is how I figured out what was going on.  

As a work around...it was suggested I use a physical loopback.  Didn't really want to do this b/c it is something that can accidentally get pulled, but in the end I did.   So I fed the Sub side out a physical output.  The only issue was tally for the sub side since it was being brought in as a physical loop back....To get around this, I put M/E Sub Clean on a keyer ( in the same M/E I was using), turned on the key ( which fired the tally), and turned the density of the keyer to zero.  W/ the density at zero, the tally still fires but you don't see the video..... I had a spare key, so this wasn't a problem.  If you are out of keyers...then you might have an issue. Not sure why I was able to renenter the output on the M/E and not have issues, but not on a DME...From playing around w/ this, I get the feeling it is a sequence of events that could also bag you.

Hope this helps.

Curt

Make sure that the CCR is enabled in the ENG SETUP/SYSTEM/INSTALL-UNIT CONFIG menu.  It is an option, and so perhaps the ENG file that you have may have "un-optioned" it.  I know that until version 8 software, you haven't been able to put an M/E into the CCR.

When all else fails, you know that you USED to have it and you know that your ENG file didn't blow away the option, try doing a system reset.