I got a 'common header' error in /includes/common.inc. Naturally I edited the file via cPanel and ensured the cursor ends on last line, last character.

After I saved the file, another error appeared:
parse error, unexpected T_DNUMBER.....includes/common.inc..line 576

Line 576# is about email addresses with ip standards like ipv4, etc, reproduced below:-
Extract from common.inc
function valid_email_address($mail) {
$user = '[a-zA-Z0-9_\-\.\+\^!#\$%&*+\/\=\?\`\|\{\}~\']+';
$domain = '(?:(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.?)+';
69.16.202.18v4 = '[0-9]{1,3}(\.[0-9]{1,3}){3}'; *** This should be ipv4.
$ipv6 = '[0-9a-fA-F]{1,4}(\:[0-9a-fA-F]{1,4}){7}';

*** somehow when I saved the common.inc file, 'ipv4' was replaced with an ip number like above 69.16...etc.

This ip number caused the error '...T_DNUMBER' because the php parser thought it was a floating point number, but with 3 points, it's an error.

The above answer was found here at Codewalkers forum.

Also see list of Php Parser Tokens

Solution
Since the file common.inc has the ip error and cannot be edited/saved, I deleted the file in cpanel and uploaded the backup copy of common.inc. It worked.

So,, make sure we frequently backup our files.