Cache location on SD Card - HELP!

[ds47uk]

My wife has just bought a tablet with an SD card slot (my nexus 7 has only a "pseudo-" SD card.
The SD card is at /mnt/external_sd and is working because I can edit a test file on it with ES File Explorer.
However when I try to change the default cache in dsub the "mnt" part of "/mnt/external_sd/dsub" is underlined in red and the cache reverts to the default.
I suspect this is a permissions problem. but have no idea what to do.

HELP!!

[daneren2005]

What is the default?

[ds47uk]

Default is /storage/emulated/0/subsonic/music
This is the same on both tablets - with and without a "real" SD card
I also tried /storage/external_sd/... but again external_sd is underlined in red
Tried uninstalling and reinstalling dsub... same

[daneren2005]

I honestly don't know then. If you say you typed it in correctly, then I don't know what to tell you. I mean, I will say tha tincluding the /music part at the end is important, but you said that you tried doing the same mount point, so I don't know. Every manufacturer decides to do it differently, so I have no idea how your's is setup or what you are doing wrong is.

[ds47uk]

@daneren2005. Thanks for looking at this. We'll just have to use the normal storage, I guess.

@other users with SD cards --- have any of you managed to use a real SD card for the cache - or have you hit the same problem? Specifically the problem is with the new (UK) Tesco Hudl tablet.