CS0234: The type or namespace name 'Xml' does not exist in the namespace 'System.Security.Cryptography' (are you missing an assembly reference?)

Hi,
we are using dotnet 2.0 framework.
I added in the above namespace in my  test.aspx.cs file.Its' working in my local machine.
When we upload the same file to production server , it showing below error 
CS0234: The type or namespace name 'Xml' does not exist in the namespace 'System.Security.Cryptography' (are you missing an assembly reference?).
I checked in Productio server Global Assemebly there are 2 versions  in C:\WINDOWS\assembly
System.Security  1.0.5000.0
System.Security  2.0.0.0
I checked in my local machine Global Assemebly there are 2 versions  in C:\WINDOWS\assembly
System.Security  2.0.0.0
Please help me.
Thanks,

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