When Amarok doesn't play audio CDs…

Amarok 1.x is quite unreliable with audio CDs. Apparently this has to do partly with configuration bugs, so the following tricks might help - or not. Depending on the engine you use, you get different error messages - "No suitable input plugin" (xine) or "could not open cd device for reading" (yauap). On the other hand, Amarok2 does not play audio CDs at all.
BTW, Amarok comes without xine plugin in openSuSE 11.0, so install the amarok-xine package to use the engine.
Possible solutions:

1. The system lacks codecs for proprietary formats. Go to http://opensuse-community.org/Restricted_Formats/ and get them via one-click install.
2. You are a victim of the infamous cdrom permissions bug - check if you can't play DVDs and burn CDs either. Some threads recommend adding your user to the "cdrom" and/or "disk" group in yast. The disk group gives raw access to all hard drives, so be careful with that. If you use the "cdrom" group, you have to give it additional permissions. See this post or the bugzilla thread.
   
3. The engine links to the wrong device. I don't know where the yauap config files are, so this is for Xine. Check for the device setting in ~/.xine/config and .kde/share/apps/amarok/xine-config (search the file for "# device used for CD audio"). Or change it in Settings->configure Amarok->Engine->xine->Default device (change the f***n' setting everywhere you can, it tends to revert sneakily). You can find out with lshw which device is used for your CD drive (sudo lshw -C disk) - or try wodim --devices. Install xine-ui (run xine, "media" tab in the Setup window) to test the settings independently.
4. Last resort: try backing up your amarok config (eg. tar ~/.kde/share/apps/amarok) and delete it. No idea if that works, my problem was always due to 1) or 3). Warning: you might lose cover collections etc. (hence the backup).
5. Are you on Amarok 2? Amarok 2 does currently not support audio CDs, as the developers do not deem it necessary - with CDs being an obsolete medium and everybody ripping them to their hard drives anyway. No, I'm not kidding. Use Amarok 1.4 if you need CD support, try Kaffeine or VLC.
   OK, new update: it's announced for amarok 2.2 or later
   

NB: the audioCD kioslave has similar issues: "An error occurred while loading audiocd:/: Device doesn't have read permissions for this account. Check the read permissions on the device". You can check this by specifying the address "audiocd:/?device=/dev/<XX>" in Konqueror (replace <XX> by any device you deem reasonable, e.g. sr0, sr1, cdrom, dvdrom, cdrom1...)
In this case, specify the correct CD device in KControl->Sound & Multimedia-> Audio CDs.