Problem:
There were following issues when trying to activate WPML plugins on a site which had content already setup but WPML installed later on:
1) Fatal error: Uncaught InvalidArgumentException: element_id and type do not match for element_id:707 the database contains post_revision while this function was called with post_nav_menu_item in /wp-content/plugins/sitepress-multilingual-cms/classes/core-abstract-classes/class-wpml-set-language.php:34
2) Trying to fix the issue by removing bad entries from "wp_icl_translations" table resolved partially but...
3) The existing content disappeared.
Solution:
A) If you have just activated the plugin that means there is no translation then you can delete "icl_sitepress_settings" from "wp_options" and then activate and reset the WPML. Please double check you have not translated the content, which should not be the case for first time install and have backup.
B) If you still see content not available in Pages/Posts, try the following after #A:
- Deactivate all plugins.
- Activated WPML only.
- Reset WPML from WPML -> Support -> Reset.
- Configure WPML accordingly.
