I have recently created a new gmail account, and transferred all contacts etc.
Since my Hero cannot read more than one account, I deleted my first account - planning to reconnect my Hero to the new account - thus enabling all the new data to connect.
However, my phone will not connect to the google server - thus I cannot get my contacts or calendar, and cannot get to the market. I'm stuck!
The message I get says: 'cannot establish a reliable data connection to the server'.
Since my Hero cannot read more than one account, I deleted my first account - planning to reconnect my Hero to the new account - thus enabling all the new data to connect.
However, my phone will not connect to the google server - thus I cannot get my contacts or calendar, and cannot get to the market. I'm stuck!
The message I get says: 'cannot establish a reliable data connection to the server'.
. Last time I had this message I had to do a factory reset. There were some guides I read no idea what was in them, for me they didnt work . I just know I spend 6 hours configuring my hero from scratch. Tried before the mybackup to backup things which failed on me too 
was long ago. So my suggestion if everything else fails, do a backup with anything you can and do a factory reset. 
)