Updating Drupal 7.2 to 7.4 Error

You can't update drupal core from the update manager, you need to update drupal core via ftp.

The upgrade guide for drupal is here http://drupal.org/upgrade you can also find information in update.txt about how to do point updates.

You can't update drupal core in the way you are trying to you need to upload the files via an ftp client to the site, ie the same way as you original transfered files when you set up the site.

From UPGRADE.TXT - these are the instructions you *NEED* to follow.

INTRODUCTION
------------
This document describes how to:

* Update your Drupal site from one minor 7.x version to another minor 7.x
version; for example, from 7.8 to 7.9, or from 7.6 to 7.10.

* Upgrade your Drupal site's major version from 6.x to 7.x.

First steps and definitions:

* If you are upgrading to Drupal version x.y, then x is known as the major
version number, and y is known as the minor version number. The download
file will be named drupal-x.y.tar.gz (or drupal-x.y.zip).

* All directories mentioned in this document are relative to the directory of
your Drupal installation.

* Make a full backup of all files, directories, and your database(s) before
starting, and save it outside your Drupal installation directory.
Instructions may be found at http://drupal.org/upgrade/backing-up-the-db

* It is wise to try an update or upgrade on a test copy of your site before
applying it to your live site. Even minor updates can cause your site's
behavior to change.

UPGRADE PROBLEMS
----------------
If you encounter errors during this process,

* Note any error messages you see.

* Restore your site to its previous state, using the file and database backups
you created before you started the upgrade process. Do not attempt to do
further upgrades on a site that had update problems.

* Consult one of the support options listed on http://drupal.org/support

More in-depth information on upgrading can be found at http://drupal.org/upgrade

MINOR VERSION UPDATES
---------------------
To update from one minor 7.x version of Drupal to any later 7.x version, after
following the instructions in the INTRODUCTION section at the top of this file:

1. Log in as a user with the permission "Administer software updates".

2. Go to Administration > Configuration > Development > Maintenance mode.
Enable the "Put site into maintenance mode" checkbox and save the
configuration.

3. Remove all old core files and directories, except for the 'sites' directory
and any custom files you added elsewhere.

If you made modifications to files like .htaccess or robots.txt, you will
need to re-apply them from your backup, after the new files are in place.

Sometimes an update includes changes to settings.php (this will be noted in
the release announcement). If that's the case, replace your old settings.php
with the new one, and copy the site-specific entries (especially the lines
giving the database name, user, and password) from the old settings.php to
the new settings.php.

4. Download the latest Drupal 7.x release from http://drupal.org to a
directory outside of your web root. Extract the archive and copy the files
into your Drupal directory.

On a typical Unix/Linux command line, use the following commands to download
and extract:

wget http://drupal.org/files/projects/drupal-x.y.tar.gz
tar -zxvf drupal-x.y.tar.gz

This creates a new directory drupal-x.y/ containing all Drupal files and
directories. Copy the files into your Drupal installation directory:

cp -R drupal-x.y/* drupal-x.y/.htaccess /path/to/your/installation

If you do not have command line access to your server, download the archive
from http://drupal.org using your web browser, extract it, and then use an
FTP client to upload the files to your web root.

5. Re-apply any modifications to files such as .htaccess or robots.txt.

6. Run update.php by visiting http://www.example.com/update.php (replace
www.example.com with your domain name). This will update the core database
tables.

If you are unable to access update.php do the following:

- Open settings.php with a text editor.

- Find the line that says:
$update_free_access = FALSE;

- Change it into:
$update_free_access = TRUE;

- Once the upgrade is done, $update_free_access must be reverted to FALSE.

7. Go to Administration > Reports > Status report. Verify that everything is
working as expected.

8. Ensure that $update_free_access is FALSE in settings.php.

9. Go to Administration > Configuration > Development > Maintenance mode.
Disable the "Put site into maintenance mode" checkbox and save the
configuration.