Writing to Excel

I'm writing av VB program that writes a lot data to an excel file. Everything works just fine for a while, and then everything just locks up. I've gone through my code a million times (and it's quite uncomplicated), so I'm suspecting that there is some form of a memory leak when writing to excel. Do you know of any way to get past this. Can I somehove emty the memory that is not being used or what?