You should provide a fully qualified name type, including your namespace. That's why you're getting a null. For example:
Form form = (Form)Activator.CreateInstance(Type.GetType("MyNameSpaceName.FmCalculate"));
And you should be able to pass any constructor parameters directly like:
Form form = (Form)Activator.CreateInstance(Type.GetType("MyNameSpaceName.FmCalculate","456", "123"));
Also, if you're using a .NET version above 2 (if I remember correctly) you should be able to use the generic function call
Activator.CreateInstance<t>()</t>
:
FmCalculate form = (FmCalculate)Activator.CreateInstance("456", "123"));
I'm going by memory here, so there may be some small inaccuracy. :-)
Please check the MSDN page on
Activator.CreateInstance()
for more details.