I've signed up to share my experience with this issue. I am using an Asus Zenfone 2 with Android 5.0 I downloaded Poweramp for Intel devices and couldn't edit tags due to the access denial. As most of you, the dialogue box did not appear from the prompt when trying to edit tags. I tried to delete a file and the dialogue box did then appear, but I still could not select the external sd card as it didn't give me the option. The sd card is a Kingston class 10 64GB which I formatted before use in the phone using Windows Explorer, exFAT format, and adding a three letter volume tag, I did not use qiuick format option and the sd card appeared in the Explorer with the volume label that I entered after formatting so the volume label is not blank. But, I did activate "download album art" in the Poweramp settings menu and behold! All my album art is now there! I don't know if that actually means that I have fixed the access problem, but as all my artist/album/genre/etc tags are managed in Windows to high level of detail, I only really need Poweramp to add the artwork when the embedding in Windows Media Player hasn't worked properly. So far, this has been the only way that I have been able to add artwork without moving full album files to the internal storeage, using iTag / Album art grabber (or similar), then moving them back to the ext sd card, which is a tedious process.