Without presenting a log file (meteohub log) this is hard to analyze.
In general 4.8a can read Vantages, so it might be something with your specific setup?
Here is a copy of the log showing a failure with 4.8a and success with 4.7b. All settings are the same only the version of Meteohub is different.
logger (09.09.2011 19:29:37): data logger (version 4.8a, build 5740) started.
logger (09.09.2011 19:29:37): connect station 0 (Vantage via USB serial).
logger (09.09.2011 19:29:37): connect station 1 (System Data via Plug-in).
logger (09.09.2011 19:29:37): station 0 (Vantage), wakeup sent.
logger (09.09.2011 19:29:37): station 0 (Vantage), internal logger activated.
logger (09.09.2011 19:29:37): station 0 (Vantage), syncing.
logger (09.09.2011 19:34:19): parent process received termination signal (15).
logger (09.09.2011 19:34:19): child process received termination signal (15).
logger (09.09.2011 19:34:19): error while waiting for data from weather stations
logger (09.09.2011 19:34:19): disconnect station 0 (Vantage).
logger (09.09.2011 19:34:19): disconnect station 1 (System Data).
logger (09.09.2011 19:34:20): data logger stopped.
logger (09.09.2011 19:35:35): data logger (version 4.7b, build 4993) started.
logger (09.09.2011 19:35:36): connect station 0 (Vantage via USB serial).
logger (09.09.2011 19:35:36): connect station 1 (System Data via Plug-in).
logger (09.09.2011 19:35:37): station 0 (Vantage), wakeup sent.
logger (09.09.2011 19:35:37): station 0 (Vantage), syncing.
logger (09.09.2011 19:35:37): station 0 (Vantage), gettime request sent.
logger (09.09.2011 19:35:37): station 0 (Vantage), time offset of Vantage: -1 minutes
logger (09.09.2011 19:35:37): station 0 (Vantage), eeprom request sent.
logger (09.09.2011 19:35:37): station 0 (Vantage), rain collector size 0.01 inch per tick.
logger (09.09.2011 19:35:37): station 0 (Vantage), transmitter 1 active as station type (#0) "ISS".
logger (09.09.2011 19:35:37): station 0 (Vantage), transmitter 2 active as station type (#4) "Wireless Anemometer".
logger (09.09.2011 19:35:37): station 0 (Vantage), no reading of Vantage's internal logger as data gap is less than 10 minutes: -831861510 secs
wmr928fulleval(09.09.2011 19:40:02): recomputation of weather data started.
wmr928fulleval(09.09.2011 20:14:11): recomputation of weather data finished: 4381561 records processed in 2045 seconds (2142 records per second)