Do CD-R's play on your player? If no, why not?

I love my Proceed MDT transport most of the time, but I'm disappointed that it won't play CD-R's. Is it a design choice or legal choice? Are there mods to change it? They play on my laserdisk player.

Design choice or maybe the way that you burn the CDs. Many players won't correctly play CDRs or if they do they skip. I've found software used with computer CD burners produces inconsistent results. My stand alone Philips CDR 880 is slow using realtime but it works almost everytime.
It may be an issue with the difference between data CD-Rs and Audio CD-Rs. Try and buy an Audio CD-R (more expensive cause royalty included) and give it a try. The Audio CD-Rs I've burned on my real-time Pioneer CDR work in car, home, portable and boombox.
Madrigal says that their Levinson M37 transport will not (or may not?) play CD-Rs, but mine does. In fact I've never had a CD-R that didn't play in the M37. Like Swampwalker, I use "Audio" CD-Rs mostly, but others have sent me computer burned CD-Rs that also play in the M37. I would think that the Proceed uses the same transport and laser reading system as the 37, but maybe not? Or is your Proceed an earlier model? Good Luck. Craig
Some player reportedtly won't play CDRs that are burned at faster speeds. I had heard that the Levinson 39 would not play CDRs and therefore did not consider buying it. I took a CDR over to a friends who has 39 and it worked, the CD I used was burned at standard speed.
My Sony DVP-9000ES plays DVD's, CD's and SACD's, but it is does NOT playing CDR's. Interesting, since Sony is one of the major music distributors.
I'll try an audio CR-R and also a CD-RW. I've even bought a "production" CD-r (I assume) of the Buckingham Nicks album. It looks like a regular CD with orignial graphics on the cd and jewel case. All of them cause the PMDT to say "no disc" on the display. Its not even about whether they skip or not. Now realize that the PMDT is a DVD player as well, which might mean they use a different color laser or something like that.
Sometimes it is a reflectivity issue. CD-Rs are only 70% as reflective (on average, not sure where I got his number) as regular CDs. CD-RWs are even worse as they are only 30% as reflective as regular CDs. Some transport optics just can't deal with the lower reflectivity of the CD-R discs. And I doubt audio vs. computer CD-R stock would make ANY difference (assuming near identical media types) in being able to play them.

usually when I can't play a disc in some random PC CDROM or a audio cd player,

1. I try a slower buring speed like 4x or 2x, barring that
2. I try a different Brand of CD-R disc, barring that
3. I try different color CD-R discs.

I can usually get te disc to play by empirically figuring out which color substrate the particular player seems to prefer (probably a reflectivity issue).

See the following link for a discussion on CD-R substrate color:
Its not vodoo, it is design. The range of laser color used in DVD players will not read CD-Rs. If you burn music onto a CD-RW disk however, it should read (theheat sensitive ink dots are a different color. A few DVD players have two separate lasers and these are the only ones that read CD-Rs and DVDs. Within CD players, the reliability of CD-R reading is very variable. Often the error correction will simply declare a disk unreadable or part of a disk (causing skips). The basic design of the transport will determine how tolerant it is. The popular mid-fi Marantz units (modded into the Ah Tjobe as well are VERY poor at reading CD-Rs, for example). I use an ARCAM Alpha 7se as a transport because it reads almost all CD-Rs. Since manufacturers don't care about this per se, you really must try out a large assortment of CD-Rs (brands, music, data, etc.) on a unit before buying if this is important to you. DVD players are just not an option unless you burn everything yourself onto CD-RW disks which are more expensive than CD-Rs and somewhat less reliable in the long-term.
My Cal Icon plays cdr's just fine
but my older Nakamichi OMS-5 and Cal Aria do not
Seems newer machines can handle and track the poorer cut cdr's. Haven't tried any on my Toshiba dvd player
When burning a cdr you must close the session before it will play. Some software allows for the burning of the disk and leaving it open so that you can add more at a later time. I don't think cdrw's will play on anything except computers. probably due to the fact of not being closed. I play cdr's on my Theta Miles and a Magnavox cd650 (circa 1988) with no problem. Remember it must be burned as an audio disk. Audio cd's are no different than standard cd's. Make sure you don't use el cheapos. Color doesn't seem to be a big factor anymore either. Here's some good links for cdr info
FWIW, My Marantz CC-47 plays CD-Rs just fine. Never an issue with me. I've used both el-cheapo $0.10 USD blanks and expensive stuff without issue. Maybe I've just been lucky? The Marantz CC-47 is a 5 disc carousel, BTW.

And as others have mentioned, both DVD players will NOT play CD-R discs.