linked drawings in layout

[Bling Keeta]

Can anyone enlighten me about this problem:
My linked drawings in layout sheets (internal and external, from View Map and from other external locations)keep getting unlinked everytime I close and open a project.
Not all of them get unlinked. The main drawings, such as floor plans, sections, elevations are ok, but some details, external pdfs etc., keep unlinked by themselves, and I had to find the source file and relink them every time.
What am I missing?

[Katalin Borszeki]

Please respond to our PM with some more specofoc questions so that we can go on researching the issue! Tx, k