Have you tried to open the files in CDWave?
I had a similar problem after a show the other night, in a rush to get my gear from the main room to the lobby where another band was going to play, I unplugged my r-44 before stopping the recording. Couldn't transfer either file...however ch3&4 I was able to open in CDWave and save to my computer with the fixed header.
Ch1&2 I was not able to recover by any method, CDWave, Audacity(raw import), Wavelab, Audiohack, pigiron's Fixwav, and a few other recovery programs just as an attempt to get them onto my computer for later retrieval. 1&2 are gone for good because I ran out of time before I had to go record over that particular card.
If mmedley's method doesn't help, Stellar Phoenix(sp?) is a pretty good recovery program. I believe I would have been able to retrieve 1&2 if my evaluation period hadn't ended...and I decided those 2ch's weren't worth the $99 dollars for the full version. You still may have problems with the headers, but that should allow you to get them on your cpu for a later fix.
Also just curious as I haven't tried myself but...have you been able to load 'good' files into Wavelab directly from the R-44? I only ask because it's usb speed seems a touch slow, I've got a little sdhc reader that blows it out of the water as far as transfer speed goes.
Good luck...let us know if you find a method of recovery...by the way, for info purposes, what brand/speed/size card did this happen with?