Sorry, I don't know what the problem with the IMDb plugin might be. Maybe nostra will have an idea.
As for TMDb plugin, I too wish it would just download the default poster. Especially considering it now seems to be the best source for quality posters. What I do is run the plugin without the option to include images. I will normally have a poster from elsewhere, but will usually replace that by using the TMDb URL to visit the site and downloading a poster manually. That process is rather easy using version 1.0.x because the image can be copied and pasted directly to the poster container.