we are trying to upgrade to the latest version of the IPB but during the process this error page pop up and i am unable to go back to the ACP anymore and the forum page as well.. Any help is appreciated !

You would need to contact you hosting company on this issue. You have an issue with a crashed table there

You can open PhpMyAdmin (if you have access), find any corrupted tables, check them and use Fix option from the dropdown.

More info - https://www.nexcess.net/help/how-to-repair-mysql-tables/

ok thanks.. i will try this 

now i have problem accessing the back admin as well .. 

If you still have crashed tables, it will cause issues in all manner of places

 

ok thanks.. i will try this 

now i have problem accessing the back admin as well .. 

Open PMA and find core_logs table. Check a few latest positions and share them with us.