Hyperlink problem

[R C]

Hello everyone again,
we are using a master document with several subdocuments.
When we originally started, the master document showed
the subdocuments as hyperlinks. Now it shows them with
regular text, and one needs to click on the small icon on the
left top corner to open the subdocument. Ctrl-and click the
document name doesn't work any more.

Any ideas?
Thank you in advance.

Regine