Can you reduce you code to a stand alone sample, like the code I provided above, that demonstrates the problem? I strongly suspect that the bug has nothing to do with writing to the spreadsheet. however, until you can provide a complete sample that demonstrates the error I don't think that we can help you much more.

It is quite likely that in the process of reducing your code to a minimum that demonstrates the problem, you will actually discover the bug.

You haven't commented on the $j == 0 issue I mentioned