I just purchased a Sansa Clip+ with firmware v01.01.05a and started copying files to the AUDIOBOOKS directory. Some .wma files from one site will not play though.
So I checked the wma file with GSpot v2.70a and found that it is using a ACELP.net codec.
0x0130 (Sipro Lab ACEPLNET) - odd that it is listed with different spellings in different boxes.
Most of my google searching seems to relate this codec to real audio but here it is a wma file. It would be especially nice to be able to use them as-is since I mostly use Linux and would rather not get into the mixing of Linux with proprietary.