SQL 2012 A significant part of sql server process memory has been paged out. This may result in a performance degradation

HI

Thank you taking sometime to help !! 

First of I have

Microsoft SQL Server 2012 (SP1) - 11.0.3128.0 (X64)
    Dec 28 2012 20:23:12
    (64-bit) on Windows NT 6.2 <X64> (Build 9200: ) (Hypervisor)

max server memory (MB)    128    2147483647    6400    6400
min server memory (MB)         0  2147483647          16          0

A significant part of sql server process memory has been paged out. This may result in a performance degradation. Duration: 1837 seconds. Working set (KB): 1062992, committed (KB): 2219688, memory utilization: 47%.

I am trying to understand this issue but not having much luck ,  this seems to happening at the most oddest of times when the environment is pretty much quiet.   Is there something I need to do or set ?

Thanks

Robert