Issue if a non-protected excel workbook is also open

When you are using an Excel protected workbook and open another non-protected workbook (normal Excel file) there is the following problem with the last one:
-It is not possible to use some options in the normal workbook such as “Save as”. You can only use “Save” and it is necessary to save a .XLSC file.

If I open firstly the non-protected workbook and afterwards the protected one, everything works correctly.

Try to open a new Excel instance. A secure workbook is not compatible with normal workbooks, it’s a technical limitation.