can you tell what type of wav it is? ie, load it into an editor and tell what bit depth it has? mpt unfortunately wont load anything but 16bit samples currently, if it is 24 or 32bit, it wont load.
or, how big is the file and how long is it?
its possible it may be a compressed wav, the .wav extension is actually a container file format so it can actually be a compressed file (such as an mp3), its just 99% of the time its uncompressed.
not sure about the error tho... on mine it just doesnt load.