I have a Nikon V1 with a 10-30 mm lens and recently purchased a +10 filter for close up work, but the camera won't focus when i use the filter. Am I doing anything wrong or is this a limitation of the camera?
Closeup filters have a tendency to make the phase detect sensor go "insane", as they are operating effectively with distances well beyond the lens working range.
Usually closeup filters are used in manual focus, and - really - it's usually better to focus by moving your position slightly rather than by acting on the focus ring (specially if it is a strong close-up filter, or even more a reversed lens).
I also don't have an special macro lens, so I use macro filters as well.
My experience, as well as the opinion of thousands of others is, that generally in macro photography, manual focus is the state of the art anyway. Because of the close distance of the camera to the subject, the depth of field gets really tiny, so the use of a tripod is mandatory. Often when you see a macro photo with a big depth of field, they usually are stacked. That means that many photos with different focus-planes are stitched together.
Here is a good tutorial http://www.youtube.com/watch?v=F3Dz34MMjQ0 on that technique.
To come back to your question: with macro filters on, cameras tend to have a hard time focusing. But, you should prefer manual focus on close ups anyway, so no need to be upset. ;-)
The Nikon V1 does know what to do. While this camera is equipped with both Phase-Detect and Contrast-Detect AF, both these work with a feedback loop. The camera measures, takes action and repeats until it detects that it has achieved focus.
You have added an unknown element in the optical path and the autofocus cannot determine what to do in all likelihood. Time to focus manually. Other filters can have the such an effect too and not just on the this camera.