If you have BigMachines integrated with Salesforce or some other Partner site you can add you partner login and password to seamlessly login between the two. This is done in the administration interface in the Users settings.

When you logon to the system and you get an error like below, this is because the partner login and/or password is wrong.

Adjust it and apply and you will get rid of this error.
BigMachines is currently not something that you as anybody can try. Only customers or to-be-customers have accounts. So I guess this post is for a rather limited amount of people. But nevertheless it might be something for the future or at least for myself I guess.