Electronic signature: transportation error

Hello all,

When I try to sign a document in the Acrobat Reader (free version) I always get the notificiation: "error during signification: the reference that is selected for signification, is invalid". Authentification works, but afterwards I receive the message 'generatiefout bij handtekeningeigenschap voor tijdstempel: onbekende trandportfout' (literal translation = 'generation error in sign characteristic for timestamp: unknown transportation error'). What is wrong? Thank you in advance for your help!

Kind regards,

Hanne Cornelis