If you get this message "Can't establish a reliable data connection to the server" when you are trying to add a gmail account there is a solution without "Hard Factory reset" 
first you must root your phone.
then you must delete the settings file.
1. adb remount
2. adb shell
3. su
4. rm /data/data/com.android.providers.settings/databases/settings.db
5.restart phone
this will reset your phone settings without hard factory reset so you can add more gmail accounts. Worked for me. I can not believe that this is happening and the only solution google is offering is to hard factory reset the phone.
BTW: I did not make this up. The credit goes to thread #16 and #49.
Issue 3477 - android - HTC Hero - can't sign Gmail account if user skips signing when initially using the phone. - Project Hosting on Google Code
This is very important and I hope this becomes a sticky.
first you must root your phone.
then you must delete the settings file.
1. adb remount
2. adb shell
3. su
4. rm /data/data/com.android.providers.settings/databases/settings.db
5.restart phone
this will reset your phone settings without hard factory reset so you can add more gmail accounts. Worked for me. I can not believe that this is happening and the only solution google is offering is to hard factory reset the phone.
BTW: I did not make this up. The credit goes to thread #16 and #49.
Issue 3477 - android - HTC Hero - can't sign Gmail account if user skips signing when initially using the phone. - Project Hosting on Google Code
This is very important and I hope this becomes a sticky.