Trying to access MongoHQ directly:
> mongo mongodb://heroku:mypassword@alex.mongohq.com:10046/myapp MongoDB shell version: 2.4.3 connecting to: mongodb://
Just see if you have $ in your password, in that scenario enclose your password with ' ' then try to connect.
e.g.
mongo mongodb://host:port/authdb -username dbusername -p 'password$123'