Hey guys,
I just did a fresh install of Rockbox (dev version ad5e5c4-151117) on my Sansa Clip+ (yes, the one that has sadly been discontinued).
My current config file is as follows:
# .cfg file created by rockbox ad5e5c4-151117 - http://www.rockbox.org
volume: -24
start directory: /<microSD1>/
playlist viewer track display: full path
database scan paths: /<microSD1>
dircache: off
tagcache_autoupdate: on
playlist catalog directory: /<microSD1>/Playlists
As you can see, I have an addon memory card, with the device name <microSD1>. The file structure is set up as such:
<microSD1>
|-- Music
|-- Playlists
My "Playlists" directory contains .m3u playlists that I have generated and copied to the device with MediaMonkey. An example playlist looks like:
I:\Music\Ministry of Sound - Ministry Of Sound Chillout Sessions XV\01 Missy Higgins - Everyone's Waiting.mp3
I:\Music\Ministry of Sound - Ministry Of Sound Chillout Sessions XV\02 Gotye - Eyes Wide Open (Yeasayer Remix).mp3
I:\Music\Ministry of Sound - Ministry Of Sound Chillout Sessions XV\03 Jessie Ware - Wildest Moments.mp3
I:\Music\Ministry of Sound - Ministry Of Sound Chillout Sessions XV\04 Major Lazer Feat. Amber Coffman - Get Free.mp3
I:\Music\Ministry of Sound - Ministry Of Sound Chillout Sessions XV\05 Frank Ocean - Thinkin Bout You.mp3
On the Clip+, I am able to open the playlist catalogue and view the tracks for a playlist:

As you can see, it is correctly displaying the paths for the files with the drive letters removed. However, when I try to actually play the tracks from the playlist, I get some brief error message (too quick for me to read anything other than "ERR"), then it skips all the tracks and exits back to the main menu. I presume that it isn't finding the files as listed in the playlist.
When I manually change some entries in the playlist, replacing the drive letter with <microSD1>,
then Rockbox is able to successfully play the tracks. But, this was definitely not necessary before I did the fresh install. Is there some setting I am missing, that tells Rockbox to start looking in <microSD1> for the relative paths to files in a playlist?