Hello Rechard,

Would you also help to check if the prn file type is register to use DDE?
If it is not using DDE, the system will not know that it should use the
existing Excel process to open the workbook. About how to register a file
type with DDE, please refer to the KB article
http://support.microsoft.com/kb/122787. It introduces three ways for your
reference.

Regards,
Jialiang Ge , remove 'online.')
Microsoft Online Community Support

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