What OS are you using? Where is the runtime (or runtimes) with M4 and V4 in it? Is this a runtime that worked well with Poser 11.0, or are you installing from scratch on a new computer? Can you post a screenshot of the file structure of the runtime Poser doesn't like?

There is no reason a runtime that worked with Poser 11.0 shouldn't work with 11.3.