Highlight and copy text suddenly stops working in ADE

Hi,

Several times when reading an e-book making highlights here and there the highlight function is disabled (grey in menu).
I don't know why it stops working ... and I don't know how to turn it on. 

The same happens with copy text function.

I use Adobe Digital Editions Version 4.5.10.186048 on PC/Windows 10.

Anyone that can help on this ?

BR /Sören