Not able to save data in Mongodb

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C#

MongoDB

I have 2 mongodb database environments in my application and am able to switch from one to the other when testing. In one of the databases am not able to insert data, when I call db.Save(...) mongodb generates an object Id, but when I go back to retrieve using the object Id the data is not there. (I don't get any error).
When I switch to the second database everything works fine. am able to insert and retrieve the data. The first database used to work and am not sure what has changed to cause this problem. any ideas?

The databases are on 2 different servers.
We using C# driver, and quite a bit of GridFs.

Thanks.