Are you using Windows XP Media Center Edition 2005 and are trying to sync content to a portable device? Does all of the content in .WMV, .WMA and .MP3 format make it over, but nothing else does? Does the rest of your content show up in the Media Center application as "An error occurred copying this file" and in Media Player 10 as "The RPC server is unavailable"?
Fear not. The solution is simple, but it is a bit of a pain in the ass. It seems that for whatever reason, on some Media Center installs, files will not properly convert and/or copy over to your portable device if the Media Center application is currently receiving a Live TV signal.
To fix it, do the following:
1) Close the Media Center application. (Right-click in the TV window to bring up the top and bottom bars [works more reliably than moving the mouse], click the "X" up in the corner.)
2) Wait 30 seconds, then bring up Task Manager. (Right Click on time, select Task Manager; or hit Ctrl-Alt-Esc.)
3) Make sure none of the following tasks are running: wmplayer.exe, ehshell.exe, wm8enc.exe. If any of those three tasks are running, click on the task and select "End Process." If you are using Process Explorer, right click on the task and select "Kill Process Tree."
4) Connect your portable device. Launch Windows Media Player 10 if it doesn't automatically launch.
5) Go to the "Sync" tab. Make sure your device is shown.
6) Click "Start Sync." Files should actually be converting.
At this point, you can hit the Big Green Button™ and start the Media Center application again. As long as you don't start watching Live TV, you should be fine using the rest of the app. However, if you start watching Live TV, chances are that the wm8enc.exe task will hang again and you'll have to start again from step 1.
I hate having to come up with workarounds for things that are supposed to just work...