Just curious, what file size does your computer show for 2007-03.wlk?
My .wlk files all seem to average around 260KB. I'm wondering if the data is missing. That's also why I was wondering if you could pull up data from April. If April is also missing I would still look for a corruption problem in the data logger that a power down and restart might fix. But if only March is missing, don't no what to make of that.
I've not used it myself but you might want to give the program at the link below a look over:http://www.ruysfamily.com/WLKReaderWriter/WLKAppDownload.html
If it opens it up the file, maybe it will provide a clue as to what is missing or damaged preventing WeatherLink from opening it. Just something to try.
Due to my station being down I'm thinking about trying to use the program to add data from the local airport to fill in the gaps in my April .wlk file. Up until this point I've never dug into WeatherLink as it has always just worked. But the gap in my continuous records going back to 2002 as a result of the ISS problem still bugs me.