Hmm. Well, as of now it's working. I received the Presto update but was initially having the same problem as before (even after rebooting just in case), with the same error message.
But now, the MP3 I'm playing (same as another poster: All About Android at
www.twit.tv/aaa) is working at 130%, 150%, 175%, 200%, and 250%.
I'll keep monitoring this, but for now it works!
Randal