#REF! after opening a spreadsheet
 

I have a spreadsheet with links to other spreadsheets
When I open my file, there is a message about re-establishing the links.
Most of the time there is no changes in the other file, so my answer is no.

At some occasion, the cells refeing to the other files show #ref! instead of
the values that were there when I last closed the file

The solution is for me to open the othe file and then close it.
The links are now reestablished
However at the next occasion, it starts all over again.

What is it and is there a solution

Thanks

AG