What is the error in a built-in module

[Ewing]

Hello, I'v a trouble to deciphre that
It occured in built-in module "documents". At first it worked correctly. Then i set up fields and layouts. When I had tried tj enter in "links" part I saw this.
What is this? How to treat it?

[Ewing]

up
nobody knows

[AlexAv]

Just turn off showing notice in php.ini file.

[catherinema]

Go to Admin->Repair->Repair Relationship. After the relationship is rebuilt, it will work fine.