Mark,
Have you heard of this from anyone else? The Yahoo price server seems to have stopped giving prices for certain Vanguard funds, in my case specifically VEIPX, VWINX, VTSAX, VTABX and VBTLX.
Oddly, Yahoo still seems to serve up prices OK for other Vanguard funds like VTIAX, VWNDX, VDIGX, and VAFAX. This has been going on for several weeks. I'll try to email you privately the log file of the price retrieve activity and failure.
Thanks,
Bart