When does it exactly crash?
Does it crash when you try to open any folder, or just when try to open an encrypted folder?
It would be great if you could send us your crash logs to support at boxcryptor dot com. Information how to located you crash logs can be found in our Knowledge Base:
https://boxcryptorsupport.uservoice.com/knowledgebase/articles/42093-where-are-iphone-ipad-app-crash-logs-located-