May I ask, are you using a WordPress multisite setup by any chance?
Usually the regular engine is the one that used to have issues, as with the index table the language code is requested from WPML tables during the indexing process.
I have looked at the index table source, where the language code is parsed, and there is actually something that might explain this issue. There is an existence check for a certain WPML function, whihc appears to be removed (I’m not sure).
Can you please try the following:
1. Open up the wp-content\plugins\ajax-search-pro\includes\classes\etc\indextable.class.php file
2. Scroll to lines 723, which should be this:
if ( function_exists( 'wpml_get_language_information' ) && class_exists('SitePress') )
3. Change that line to:
if ( class_exists('SitePress') )
4. Save the file.
5. Re-create the index table. Just click on the Create new index button, and it will delete the existing one.
It the problem was the missing function check, then there is a chance that this might resolve the problem. Please let me know, and I will incorporate this change to the latest release.Best,
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