"Setup failed: Sequence contains more than one element" error means that settings.txt file already exist in your application, but it's empty due to unsuccessful installation. You need to remove it from App_Data folder.
Mentioned error is probably related with server. Maybe it has some limits and it didn't make all inserts. Where do you have your MongoDB hosting?
If you are deploying GrandNode on Linux, did you restart application after successful installation?
As you may see on our demo, in the default installation this problem doesn't exist.
I have installed monodb 3.5.6 community edition. Please note the only difference I'm doing here vs nopCommerse is on installation screen, I'm not providing user name and password for database connection as monodb does not require it. It created the database successfully with probably all the tables so connection is probably not the issue.
Please click the link below to see the error screen shot.