Capella studio java.lang.NoClassDefFoundError

Dear all,
I am actually working on a viewpoint that extends the physical architecture page and add a section containing at least one activity.
I am trying to open the diagram editor programmatically after pressing the link of the activity in the activity explorer.
After generating the viewpoint to start working on the activity explorer and fill generated stubs with my business code, I noticed that there is messing plugins like sirius ui plugin that contains the DialectUIManager and the capella common helpers plugin that contains the TransactionHelper
The two classes that help me create the representation and execute it to be able to open the editor are missing in this case.
However, I could find the two plugins in the capella studio plugins folder and I have added them to the build path of the activity explorer generated project.
After coding the editor opening part with no compiler errors, I’m having troubles during run-time of the capella project.
Actually, when I click the activity link, I get the error below and nothing happens after that.
Personally, I think that comes out because of the messing plugins in the generated projects of the view point.
Is there any explanation for that?

I could solve the problem. Actually, the NoClassDefFoundError is a run time error. I used to add the TranscationHelper class to the imported packages using the eclipse suggestions instead of adding it to the required bundles. The attached picture shows that.
When I used to add the missing classes to the imported packages, it solves the compilation errors but during the run time the JVM doesn’t find them so it throws the NoDefClassError.