Note: I've posted the same info at openMSX forum, but I haven't seen much activity there, so I'll report also here. I've no user at Sourceforge, so I cannot use the regular bugreporting tools. Sorry for any inconvenience.
Using openmsx 0.6.3 for Windows I cannot load WAV files. I have tried both using Catapult and also from command line, using the command -cassetteplayer FILE.WAV. It crashes indicating "not a valid CAS file". Evidently, it is not a CAS but a WAV and therefore it cannot work.
If I try to load the WAV file from the openmsx console, using CASSETTEPLAYER [INSERT] FILE.WAV it also indicates "not a valid CAS file".
Maybe I'm not doing it ok, but apparently WAVs cannot be loaded. At least, not in the Windows version
Just for your information, all the WAV files were produced with WAVER, that used to work fine with older versions of openmsx.
Apparently, everything works fine in openmsx 0.6.2/Windows. Therefore, the problem is located in the newest version, 0.6.3. AFAIK, it tries to analyze the WAV file as a CAS file and of course, the format is not valid. I guess that the solution should be easy, but again, I haven't messed with the sources