Error: You must enter a valid separator page (due to invalid filename entered).

Error:

You must enter a valid separator page

Cause:

When the 'General' tab is selected in the 'Properties' dialog box to configure the printer to use a separator page, and an invalid filename is entered on the 'Separator page' box, an error message is displayed.
After clicking the 'OK' button to clear the error message, the 'Details' tab is automatically selected as the current tab.

Solution:

Manually select the 'General' tab and then type a valid filename in the 'Separator' page box.