Version 4.0 of Magento WordPress Integration includes some significant changes to the internals of the extension. While these changes won't cause much difference in frontend functionality, they will allow for some great new additions to the module in the months to come. If you haven't customised the extension by copying templates to your custom theme and modifying them, upgrading won't be a problem. If you have done this, upgrading may require a little bit more of your attention.
If you would rather not do this yourself, you can purchase the support service for Magento WordPress Integration and we can upgrade the extension for you.
What's Changed in Version 4.0
The most significant changes are the removal of the following classes:
The Page model has been completely removed from the extension with pages now being displayed using the Post model with a post type of 'page'.
Both the post category and post tag classes have been removed with categories and tags being displayed by the Fishpig_Wordpress_Model_Term class.
Fixing Errors After Upgrading
If you have upgraded Magento WordPress Integration from a version earlier than 4.0 to either 4.0 or an even newer version, you may notice some errors. If this is the case, let's look at how to resolve them.
The first thing to do is to disable the Magento cache and compiler (if enabled). It's also worth pointing out that you should ensure that PHP/Magento is configured to display any error messages, which you can do by reading this.
You should also upgrade any FishPig extensions you have installed.
Now that the errors are displaying and the cache is disabled, open up your FTP client and connect to your site. Go to your custom theme and check the 'template' directory for a folder called 'wordpress'. If you find this folder, rename it to 'wordpress.old'. This will allow the latest version of the templates to be used. Do the same for the 'wordpress.xml' file, which should be in your custom theme's 'layout' directory. Rename this file to wordpress.xml. With these changes made, refresh the page containing the error. This should fix the error message.
While this has fixed the error, the templates you just removed (by renaming the parent folder) may have had some changes that you made to the design that you want to keep. If this is the case, you will have to fix each error individually until the page loads correctly. You can compare the template with the error message with the latest version of the template (these are stored in app/design/frontend/base/default/template/wordpress/), which should help you identify the problem and how to fix it.
If you need support for anything relating to version 4.0 upgrade, please purchase the support service for Magento WordPress Integration.