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Administration display is wonky
On first load after making the upgrade, administration pages might look weird: because your web browser caches files, it is probably using the old CSS and JavaScript files instead of the new ones.
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The name of the default theme has been changed from "defaultprestashop" to "prestashopdefault". If you were using the default theme, rename the default theme's folder from "prestashopdefault" to "defaultprestashop", and everything should work again. You can find that folder in your /themes folder.
Some modules are not working
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Incompatible module
In some rare cases, some modules are may not be compatible with new the latest version of PrestaShop. You should contact the company / person that provided you with this module to request a few code changes to bring it up to date.
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