Dunno about 'failed to convert', but there is no point in converting from 64 to 128 anyway - yes, you lose sound quality.
Every time you encode to a lossy format eg wma, mp3, a certain amount of information is thrown away. This is stuff that you are supposed not to be able to hear - its what allows the filesize to be reduced without an apparent loss in quality.
Mostly of course it works, but if you reduce the bitrate too much you are going to throw away too much and be left with a really poor quality sound. Also, a bit like repeatedly photocopying a piece of paper, if you convert from 64 to 128 you are never going to get back the bits that were thrown away when you converted to 64 in the first place.
If you have the space, best to initially rip your songs to a lossless format, eg ape. With this you can 'uncompress' your files to get exactly what was on the CD, then reconvert it to a lossy format with a quality that suits your ears.
You will get loads of advice here on this from better experts than me, I predict.
Bottom line: Never reencode a wma file you have already ripped. Hope that makes sense.