Problems aftre user change on server

I needed to change the user that had right on a ftp domain on my server.

After a have changed the user and moved all the files, the open cart stopped working fine and a have this error on the main page:
Warning: session_start(): open(/tmp/sess_SZLDKuHEPVpeRuyqmtaAf3, O_RDWR) failed: Permission denied (13) in /home/prichindel/prichindel-shop.ro/system/library/session.php on line 21Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/prichindel/prichindel-shop.ro/index.php:98) in /home/prichindel/prichindel-shop.ro/system/library/session.php on line 21

And I can't acces admin page.

PLEASE HELP!

did you get any help on this? i get the same error and can not access admin page.

Whenever this happens, it is an indication that something is wrong with the server settings or he is poorly configured.
Folders and files and permissions are written with the FTP-user.
Changing now these folders and files by another FTP-user should have no impact if the server is build correct.
Which seems not to be true in this case.

To get the shop working again you have to assign now the new user rights and permissions and owner settings to all of those folders and files.
Which will be done usually automatically by the server if correct configured.
But this happens many times at cheap providers.

Either assign them by yourself or ask the provider to do so.