Unexpected character in input: '\' (ASCII=92) state=1

My client says he is getting this error using my script:

Warning: Unexpected character in input: '\' (ASCII=92) state=1 in /path/to//header.php  on line 34
Parse error: syntax error, unexpected T_STRING, expecting T_CONSTANT_ENCAPSED_STRING or '(' in/path/to/header.php  on line 34

The line 34 in header.php is just use \Main\Class;

Now, I told him he has to have PHP >= 5.3.0 and he says his PHP version is 5.3.24

What could be the problem?

EDIT: The lines before and after

30. // Define absolute path
31. define("ABSPATH", $abs_path);
32. $_SESSION["abs_path"] = ABSPATH;
33. 
34. use \CNS\main\CNS;
35. $cns = new CNS();

EDIT 2:

He sent me this:

Program     Version
Apache:     2.2.24
CentOS:     CentOS release 6.4 (Final)
cPanel:     11.36.1 (build 8)
Curl:       7.12.1
MySQL       5.5.30
phpMyAdmin  3.5.5
Python:     2.6.6
Program     Version
Perl:       5.8.8
**PHP:        5.3.24**
ionCube Loader:     4.2.2
Zend Optimizer:     3.3.9
Ruby:       1.8.7
Rails:      3.2.8
OpenSSL:    1.0.0-fips

This happens if you are trying to use namespaces but do not have PHP 5.3. PHP 5.2 and below don't support namespaces and throw this error when they see the backslash.

-- Edit: mixed up the versions. It's 5.2 and below that don't have namespaces, if I'm not mistaken.

Now, I told him he has to have PHP >= 5.3.0 and he says his PHP version is 5.3.24

What could be the problem?

His PHP version is actually < 5.3.0, whether he knows that or not.

See the error occurring on many PHP versions.

If you get 'unexpected T_STRING' error after your mentioned error, you need to install PHP 5.4+

Ask him to create a file with phpinfo(). He probably doesn't have PHP version >= 5.3.0.