Simulation in Catia of different versions - vb.net

Question

My simulation is run in the dum kinetics module, the code was written in vb automation in Visual studio 2010 environment. My problem is when I ran the simulation in Catia R18, the process was completely smooth and successful, but when I tried to run it in a different version, like R20 or R21, an error occurs.
Through the breakpoint, I found out that the error was caused by the failure of acquiring the "Mechanisms" in the product of Catia. Here is the code :
theMechanism = product1.GetTechnologialObject("Mechanisms")
When the breakpoint executes this sentence, variable theMechanism shows "Nothing".
The only way I know to solve this problem is run the code again in visual studio 2012 environment, then the simulation works in Catia R20 or R21, but after that you can't run the simulation in Catia R18, if you want to revert back to the version R18, you have to run the code in visual studio 2010.
Can anyone explain what is the cause of the conflict between versions of Catia and give me a solution for this? Thanks!

Answer 1

I think You have defined theMechanism as Mechanism Instead try it as variant.

Answer 2

product1.GetTechnologialObject("Mechanisms")
Returns Mechanisms, not Mechanism.
So:
theMechanisms = product1.GetTechnologialObject("Mechanisms")
theMechanism = theMechanisms.Item(1)
Also, if you have multiple CATIA versions installed on one PC, check which one is the main one (check RegServer command). Check if Visual Studio versions have references to the same CATIA version or not. In theory, they should, if you didn't change the main CATIA version.
You could also get the mechanism through the following:
KinematicsWorkbench kinWork = (KinematicsWorkbench)productDocument1.GetWorkbench("KinematicsWorkbench");
Mechanisms mechanisms = kinWork.Mechanisms;
Mechanism mechanism = mechanisms.Item(1);
This is C# code, but the VB.NET code should be nearly identical outside of some slight syntactical differences.
EDIT:
If multiple CATIA versions are installed on one machine, the last one which is installed will be a default one. To change a default CATIA version, follow these points (taken from here):
Open cmd.exe
Change Directory in the CMD window by typing “CD /code/bin” (Typically CD C:\Program Files\Dassault
Systemes\Bxx\win_b64\code\bin) and then press Enter.
In the next line type in “CNEXT.exe /regserver” and press Enter.
This will appear to have done nothing but will display the next line. At this stage restart the machine and then enjoy.