'System.Type' does not contain a definition for 'GenericTypeArguments' with (dynamic)

I am trying to get the type of a dynamic linq column using

var args = ((dynamic)linqColumn).PropertyType.GenericTypeArguments;

then comparing on the possible types names :

if (args.Length > 0 && args[0].Name == "DateTime")
    ProcessDateTimeType();
else if (args.Length > 0 && args[0].Name == "Double")
    ProcessDoubleType();

This works on a Windows Vista with .NET 4.0, but does not work with a Windows Server 2003 also with .NET 4.0. An error 'System.Type' does not contain a definition for 'GenericTypeArguments' is throwed.

Any idea ?

Remarks

• linqColumn is obtained via var linqColumn = linqTableType.GetProperty("COLNAME");
• linqTableType is obtained via 'Type linqTableType = Type.GetType("MYNAMESPACE." + "TABLENAME");
• Code is executed inside a web service