Admin failure.....Urgent Help Requested

My ISP did some migration and now the backend is showing these errors and does not load. It gives these errors. however the frontend is working and orders can be placed. Please advice

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/indhobis/public_html/shop/admin/includes/functions/general.php:6509) in /home/indhobis/public_html/shop/includes/functions/sessions.php on line 108

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/indhobis/public_html/shop/admin/includes/functions/general.php:6509) in /home/indhobis/public_html/shop/includes/functions/sessions.php on line 108

Warning: define() expects at least 2 parameters, 1 given in /home/indhobis/public_html/shop/admin/includes/languages/english/email_extras.php on line 77

Warning: Cannot modify header information - headers already sent by (output started at /home/indhobis/public_html/shop/admin/includes/functions/general.php:6509) in /home/indhobis/public_html/shop/admin/includes/init_includes/init_templates.php on line 36

Warning: Cannot modify header information - headers already sent by (output started at /home/indhobis/public_html/shop/admin/includes/functions/general.php:6509) in /home/indhobis/public_html/shop/admin/includes/functions/general.php on line 41

Thanks

(output started at /home/indhobis/public_html/shop/admin/includes/functions/general.php:6509) 

"6509" refers to the line number and this file should only have about 3000 lines

I suspect that this file is corrupt

If you have a copy/backup - replace it or get a new distribution that is the same version as you are running from the download link on the home page of this site, expand it locally and FTP a new copy to your server

No its not because of file corruption because the error occours even with replacing all the zencart files with backup files

My ISP did some migration...

No its not because of file corruption because the error occours even with replacing all the zencart files with backup files
So if it did work and now does not, even after replacing files, why are you not taking this up with your ISP?
How is it a ZenCart issue?

tried replacing about 4-5 files that showed the errors and now its working.

Kobra...sorry I never said it was a zencart issue. I just needed someone who was more knowledgeable than me..Thanks for the advice

Always start with the first one, as even one file can spawn a battery of errors
If you still have errors thsy should start with a different file