if you are reading sheet SITC3, dt2 will be similar to this image.
Yes, I get the same. I get SITC1, SITC3, & SITC3 to process.
At the moment I'd guess that you have a non-compliant file. There may be a typo or something in the file but I don't know enough about {data.tree} or the UN's file structures to know how to check it.
Maybe a query to the responsible people at the UN?
I think you have found enough to bring the issue to UNSD's attention. If you can successfully convert 3 out of 4 data.frames then this seems enough to alert UNSD to a serious problem in one of their data sets.