Can chronic diarrhea cause an inability to lose weight?

No. It is more the other way around. Chronic diarrhea can be a sign of metabolic disease or a sign that you aren't absorbing nutrients properly. You should see you doctor for workup of the chronic diarrhea.
No. Chronic diarrhea may be due to various medical conditions, but should not cause an inability to lose weight. Because an "inability to lose weight" requires a person to continue eating and/or drinking, there may not exist any medical conditions in which one has a true "inability to lose weight" once his access to foods and drinks is restricted. Chronic diarrhea should be evaluated by a doctor.