Unable to access the module error while trying to simulate a simple PLC Lad program
One "trick" that often works is to type some of the exact error message into a search engine (with quotes around it) and see what comes up. In your case I find this in the Siemens PLC forum: 

"I go to Options->Set PG/PC interface and select PC Adapter(MPI)...After that, PLCSIM going to work... "