Personal robots and screen agents can be equipped with social abilities to facilitate interaction. This paper describes our research on the influence of these abilities on elderly user's acceptance of such a system. Experiments were set up in eldercare institutions where a robotic and screen agent with simulated conversational capabilities were used in a Wizard of Oz experiment. Both agents were used with two conditions: a more socially communicative (the agent made use of a larger set of social abilities in interaction) and a less socially communicative interface. Results show that participants who were confronted with the more socially communicative version of the robotic agent felt more comfortable and were more expressive in communicating with it. This suggests that the more socially communicative condition would be more likely to be accepted as a conversational partner. This effect was less strong however, with the screen agent, suggesting that embodiment plays a role in this. Furthermore, results did show a correlation between social abilities as perceived by participants and some aspects of technology acceptance for both systems, but this did not relate to the more and less socially communicative conditions. Evaluating the experiments and specifically the use of our acceptance model we suggest that this particular context of robotic and screen agents for elderly users requires the development of a more appropriate acceptance model which not only features technology acceptance, but also conversational acceptance.