This thread is resolved. Here is a description of the problem and solution.
The wp_icl_string_pages table in the DB is damaged.
Please, try the troubleshooting section.
Go to WPML -> Support -> Troubleshooting (link)
Once on the troubleshooting screen press the following button and check if it helps.
- Recreate ST DB cache tables
This is the technical support forum for WPML - the multilingual WordPress plugin.