You may have encountered a situation in nTop Platform where you try to add your parts to a block that accepts a list of inputs, and it won't let you.
This is because the input you are trying to add looks like "Block Name (1)". Somewhere, a List of One was created. Lists of one are sometimes unintentionally created by the user, or during CAD/Part importing. They can be converted to singular entities by either dragging the entity out of the Properties tab of the Info Panel or by using the List Element block.
To drag the entity out, open up the Properties tab, expand until you find the part, and drag the part chip into the Notebook. This will create a block in the Notebook that doesn't have a list.