I think I just encountered this problem. Or at least I think my problem is similar to the one described here.
I use an Arduino Mega. All the SD functions fail and hang-up when my program reaches about 83K in size. After searching the Internet on this problem, I came across this thread on this forum. After browsing over the postings, I check my functions over and over again, I check my array indices again and did not find anything wrong.
Anyway, I just took Mr. fat16lib's advice and check the array indices again. I may have missed something, so to be safe I increased the all the arrays indices by 1 or more elements and all the SD functions start to works again. I think my problem is due the Array memory overflow. I have yet to figure out which array is causing the problem, but for now, I am just happy the problem is fixed.