The current open innovation literature needs to be complemented with work on the managerial challenges faced by companies working with an innovation intermediary to solve research and development (R&D) problems. Based on an exploratory case study design, we investigate these managerial challenges in seven chemical companies working with the same innovation intermediary. Three recurring challenges were identified in all companies: (1) enlisting internal scientists to work with the innovation intermediary; (2) selecting the right problems; and (3) formulating problems so as to enable novel solutions. Based on the knowledge management literature, we explain how these challenges arise out of scientists' different work practices in internal vs. external R&D problem solving and we identify and discuss a number of remedies to these challenges.