Multiplication of Dotnet double

I have defined three dotnet variables of type system.double.

System.Double.'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

How do I multiply these together? if I try and perform the following double1 := double2 * double3; I get the following error when compiling

Type conversion is not possible because one of the operators contains an invalid type. Dotnet * Dotnet