The problem could be specific to Excel 2010, I don't know. Those kinds of errors are unfortunately all too frequent when talking to MS Office components. Word is even worse. Unfortunately, I lost the source code for that project when my computer was stolen and haven't gotten around to rewriting it since, so have no way to look into it. Sorry.
You can, however, have the utility output to a text file rather than to Excel. Append -TEXT to the command line. The data file can then be imported into Excel.