I'm using MC6. Have Guitars assigned to a Guitar Bus, drums to Drum Bus, Vocals to Vocal Bus, and Bass to a Bass Bus. Now, I'm "hacking" my way through mixing our recordings, but after a couple years, think I'm doing ok for what little time I can dedicate to this process. I had read somewhere that a wee-bit of reverb to each "instrument" would help blend them all together. So when I noticed the Reverb Bus and that I could assign Sends from that to the instrument buses, I thought "Ah-Ha!". Well, I'm having a couple issues with this: 1. I'm not always able to add sends to all of the buses. One song, I can add all 4. Another, maybe 2. Next one, 1, and some I can't add any sends. 2. So, I created a new Bus, called it VERB, added the StudioVerb effect to it, and I can add sends to all 4 buses from here. Sending the VERB bus to the Master Bus. It doesn't appear that the effect is having any "effect" on anything. 3. When I reopen a project to which I have added sends from either Reverb, or my own VERB bus, those sends are gone. Yes, I saved the project. Would appreciate any help in clearing up my ignorance.

I simply drop the reverb plug in into the bus's FX Bin.  That puts the verb on everything routed through that bus. 

I don't mess with sends. Didn't even know that were available in MC6, but doing it the way I mentioned works fine. 

If you can add them and then save the project and they are not there... and/or add them to various projects and none seem to allow the same number, I suspect that it might be some sort of bug..... since MC6 is a "smaller" version of X1.... so perhaps something allows the sends to work some of the time and not on a consistent basis. (just a guess here) 

Try using the bins and drop the plugs into the bins....see how that works. It has never failed on me to work that way. 

If I am reading this correctly, it looks like you have the routing backwards.
You don't send from the Reverb bus to the other buses(or tracks).
You send from them to the Reverb bus.
There should not be any sends from the Reverb bus at all. The Reverb bus output should go to your Master bus.

Your signal path should go something like this:
Guitar tracks ......> Guitar Bus....Output > ........................................................Master Bus
                         .                        Send to Reverb Bus  > Reverb Bus ...Output >Master Bus

Make sure there is actually a reverb effect in the FX bin of the Reverb bus. it may just be pre labeled for convenience.

Have a look at this:
http://forum.cakewalk.com/tm.aspx?m=1302521

It was written for an older Cakewalk version, so it looks a little different, but the idea is the same.

A golden oldie from RobertB.
 

Amateurs 2 cents:
Be very careful in adding different instances of reverbs to each bus/instrument. Due to the nature of the different sounds (hit vs. stringy, high vs. low) it can make things messy. Often the reverb is added only to the higher frequencies of an instrument, because reverb on low sounds, bass in particular, can create audio-porridge. A nice sounding reverb on one instrument can sabotage the mix. At least for an amateur like me more than two-three, sometimes four, reverbs in one project (for example reverb on snare and guitar solo, Perfect space on vocals and subtly on master bus) is the maximum I can handle.

A power snare, female vocal, strings or guitar lead can tolerate a lot of reverb/delay on top of a mix which already has general reverb, but if the purpose of the reverb is to position the instruments in the same acoustic space, glue them, it's best used only on master bus or on buses for several instruments.

Thanks guys. It appears I was just doing this wrong, which I always thought was the possible problem. :)