When initializing the simulation, PTV Vissim freezes on 'Build node structure... Node n'.

This problem usually occurs when nodes are missing in the network. In such cases, there are too many possible paths/edges, and PTV Vissim cannot build the abstract network graph. Add the necessary nodes; one node per intersection generally works.
For more information on how to properly code nodes for dynamic assignment, in PTV Vissim, click Help > PTV Vissim Help and refer to the section 'Building an Abstract Network Graph' and its subsections.