Only text can be pasted into this type of field
What happened
You tried to paste something other than text, such as a document link, into a plain text field, such as the Email field in a Contact document in your Contacts.
Note: If you paste text with rich attributes such as bold or
italic into this field, the text will be pasted, but will be plain
(IBM® Notes® strips the attributes).
What you can do
Either don't use document links in this field, or, if you're the application designer, change this field to a rich-text field.