ESEF.3.1.1.extensionTaxonomyWrongFilesStructure - Each linkbase type MUST be provided in a separate linkbase file: cal linkbase has no calculationLink element.

This error will appear when the source document (your statements) don't contain calculations. ESEF files have to contain calculations, not only the sum of the calculations. Otherwise the XBRL engine can not validate the sum of the calculations. 

This is also reported in the checks done while running the conversion into an ESEF report.

The calculations are usually imported together with the data from Excel if your Excel file contains formulas.

If it is difficult to add calculations into your Excel file (for example because they are generated from another system), we can on request adapt your Tangelo to specify the calculations from within Tangelo.

Advise: Review the source files and add the calculations. Formulas / calculations are mandatory for all financial statements.