I've imported my fair share of content using the Node Import module and one thing I always watch out for is empty data. Spreadsheet with blank columns that need to be imported always seem to cause problems.
One trick I've learned to help squash some of the issues is to add an extra "END" column at the end of the data, with each row of the END column populated with a "1". Not only does this help keep the rows aligned, but it also gives me a quick way to make sure nothing wonky is going on when I'm working through the various steps of the Node Import module.
Another tip on this topic has to do with multiline text fields. If you're going to be using linefeeds as the row delimiter, be sure to convert any intra-field linefeeds to something else (HTML breaks is usually a good one).