As of the last week or so, I have started to get freezes (of MC, not the whole PC), but only with Internet Radio stations, not local files, and not files on the LAN. No changes in the PC, but there have been Windows Updates. I tried MC19 (build 221) and same thing as with MC20 (build 10).
Does JRiver MC use UDP in some way? The problem is exactly as described in:
http://support.microsoft.com/kb/307650which refers to "Windows Media Player". I do have ADSL. The PC is connected to the router with a Gigabit Ethernet wired connection.
UPDATE: On the same PC, I used the built-in web player at wwoz.org ("listen") in Firefox, and it worked fine without problems for 2 hours. Then I closed the browser, started MC20 and tuned to WWOZ in MC20 (I have a button that tunes the URL
http://50.31.135.43:80/wwoz-hi.mp3 ) and it froze "buffering..." within about 10 minutes. (And, until I killed the frozen MC20 process, Firefox was not able to be started again.)