MongoDB "j must be a numeric or boolean value"

I have set up my own local mongodb instance (v. 3.0.2) in ubuntu local version (14.10) and I am using genghis (version 2.3.11) for rendering. My program is capable of creating new documents in the database, but when I try to save the newly created document or delete the document in genghis it always returns "j must be a numeric or boolean value", but it creates / deletes the document anyway. The error does not appear when displaying the document. The only thing I could find when trying to find a solution on google was the following: https://github.com/mongodb/mongo/blob/master/src/mongo/db/write_concern_options.cpp , which makes me think it is the problem is with my mongodb setup (and has nothing to do with genghis), but I don't know how to resolve it.