If (with video file loaded) under Options > Filters > Advanced now still showing "DivX Decoder Filter", you can reach its "Quality settings" window through there by clicking on the [+] in front of it and then selecting "Quality settings".
If "Support Generic Mpeg-4" is checked,
uncheck it.
Exit BSPlayer and retry. (Dont't think you need to restart your PC)
Check (under filters) if BSPlayer is now using XviD-codec.