I have a new Android phone (Razer Phone) and have been getting all of my emulators and ROMs/ISOs set up. I had this problem on both DraStic with NDS ROMs and on Classic Boy/My Boy with GBA ROMs. For some reason when I have them on my SD card they will not load properly to be played, but when I moved them to internal storage on my phone they worked fine. This has not been a problem with all of my other ROMs (SNES/Genesis/NES/GBC) but for some reason on these two platforms I can not store them...
ROMs load from Phone but not Micro SD
ROMs load from Phone but not Micro SD