Hi, this is a pretty old thread you have posted on, you may not get a reply from the original poster.
I think the obvious things to try are:
1. Reduce the rate at which you request objects and see if that helps.
2. Write a test program using the LEGO firmware and programming tools and try and reproduce the problem (or use NXC if you are more familiar with it).
3. Try a different sensor port (especially if you are using port 4, which has different hardware to the other ports).
leJOS news https://lejosnews.wordpress.com/