BPC 7.5 NW SP5 : XLTX file won't open

Dear Experts,

I want to save a specified format (via FormatRange). Unfortunately it won't save in XLT format. If I save the file in XLTX format and open it with regular Excel, formatting is ok.

If I try to open the XLTX file via BPC Excel, nothing happens (not even an error message).

I set up the WebAdmin so XLTX is included the "DEFAULT_EXTENSIONS".

Am I missing something?

Best Regards,

Axel