Why does this happen?? The site was created on one server then moved to another server or your hosting company moves your site to another server. Log into your CPanel and go to your public_html folder and look for the configuration.php (Joomla),  wp-config.php (Wordpress), settings.php (Druple), etc...

Once you locate the file look in the very right column (the permissions column) and it should be set to 444 (is a read only setting).  You will need to change this to a writable permission to change this file.

Select the file, click the icon "Change Permissions" and then check the boxes until the permissions are writable and executable, 755 or above.

On my server I can not set any file to 777 as this will cause errors and is a failsafe setup on the server. 755 is good enough to do the job.

Remember that after making your edits to the file you will need to change the permissions back to 444 to keep your site secure.

After you have changed the permissions select the file and click the "Edit" button.

You will see in the very top of the browser the true location of the file.  /home6/ or it could be /home/ or something like that.

Scroll down the file until you located the lines of text that describe the location of the log_path and tmp_path.  The "home" location must match the true location at the top of the browser window.  If it does not match you will need to change it.

You can also change the log_path and tmp_path to match like the screen shot on the right.  This might actually be better if you develop on one server and then move to another server.