This is a really specific issue of the application and it can be related with any of the plugins or the configuration you have in Redmine. Bitnami packages and configures already existing applications. We can only offer support and help on basic and most frequent application configurations. Always based on the default configuration or on our guides.
We suggest you to post your question on the official support forums of the application or to promote this thread in social networks so others can help you with your issue.