This error occurs due to a limitation in the taxonomy, which affects extensions and calculations in the cashflow. What happened, is that something has occurred in your annual financial report, which ESMA has not taken into consideration when drafting the taxonomy.
XBRL only allows certain, simple, forms in calculations, and in cash flow statements issuers will often transgress the rules set forth by ESMA. The problem here is, that what is being done by the issuers is actually mathematically correct but even so, XBRL returns an error of an illegal calculation.
The only current solution to this issue is a “workaround” where the affected formula is removed, as this will make the file convertible and usable.
If you experience this issue you can contact firstname.lastname@example.org and we will help you sort it out.