Diagnosis
On the alternative overview (all alternatives for a BOM), you haveselected a number of alternatives and chosen menu option Goto--> Header overvw.
You are now looking at the header overview (historical headers) of oneof the selected alternatives, and want to get the header overview ofthe previous selected alternative using function Alt-.
As all the other selected alternatives only have one header, thismessage appears.

Procedure
You have three options:
If you want to move in the other direction, choose function Alt-.
If you want to go back to the alternative overview and maybe reselect,press function key F3.
If you want to display the header detail screen directly for eachselected alternative which only has one header, and the header overviewfor each selected alternative which has more than one header(historical headers), choose menu function Header full orHeader qty/long textinstead of Header overview.