I've had this happen. It is usually a corrupted poser.ini file. Find this, delete it, then run poser again. It will create a new ini file. You'll have to reimport your runtimes and reset your defaults, but it ought to clear up your issues.

In the future, you might make a copy of this newly created ini file after you get it defaulted the way you want. This way, if it gets corrupted, you can delete the corrupted version and replace it with a new copy of the good version you've just created. Saves a lot of time.

Also, try selecting the render screen BEFORE you tell the program to render. Sometimes this cleans the problem up.