Default why does Google music (5.4) prompt "no space available" when my external SD has space

Hi

I have a galaxy S2 with Wanamlite V14.6 (android 4.1.2). Google Music 5.4.1409 prompts "no space available" when I try to download offline, whereas I have an external sd crad of 32GB with 30GB free. Can you help me please ?

Thanks
SGS2
ROM: stock WanamLite...cwm flashable and very good.