I have a Mac Air running El Capitan and a Windows 10 dual boot. I have a memory card (Transend Jetdrive 128gb)mounted as Mac OS extended. This is used just for my iTunes where read/write speed isn’t that important. I can read these files under both Mac and Windows.
I would like to create a folder for Dropbox on this drive under Windows but it states “Destination Folder Access Denied”. I have it shared to everyone under both Windows and Mac but no joy.

Anyone have any ideas what I’m doing wrong?

I’ve a similar issue and it seems that mac can’t write windows ntfs file system format and vice versa. You could format the drive to FAT but I’ve heard it’s horrendously slow. What about running Windows as a virtual machine in mac using parallels? You can share folders that way.

I have Parallels but found it nothing but trouble so went the boot camp option.

What trouble did you have with Parallels? I use it for AutoCAD and Inventor on my MacBook and, apart from suffering the poor design of Windows, everything runs OK for me.

As drslow says, it’s probably the Journaled format that’s the problem. I have a permanently fitted micro-SD card, formatted OS Extended, for Lightroom and my iTunes – it doesn’t even show up as a drive in Windows/Parallels.

On MB Pro (i7 and 16GB) everything seemed to run slow and connecting to networked drives was hit and miss. Maximising the memory and mapping the network drives didn’t really help. Tried boot camp and never touched Parallels again. On the MB Air didn’t even bother installing Parallels.

Paragon do an NTFS preference pane that will allow the Mac to read/write to this format. It isn’t cheap but it does work. The free versions don’t work as well.

Parallels worked for me with a win10 VM. My mac is 2015 MacBook Pro i5 with 8gb. No performance issues. Have you tried formatting as FAT? Would be interested to hear results.

Dropbox won’t allow you to use a removable drive for the Dropbox folder. The workaround for this is to mount it as a folder on a non-removable drive. If you Google, you’ll find instructions on how to set that up.

Tried a program under trial called MacDrive that allows you to read/write onto MAC OS drives as if they were NTFS. Seemed pretty quick so would have bought it but as Holst pointed out Dropbox does’t allow you to have the Dropbox folder location on removable media. Installed under MAC OS and you can have the folder location on removable media 🙄
Decided I would just install the Dropbox to the internal drive on the Windows partition but would need to extend it to do so. Tiredness or too many glasses of wine and I cocked it up and lost the all the windows files, only program files so nothing that can’t be corrected with a bit of time.
Thought I’d try the Parallels again and it is working really well much better than it did on the MB Pro despite it using the recommended settings which is less than 2gb memory allocated. I have Dropbox installed on the Transcend Jetdrive, which although removable never is. I can access this through both Windows or OS and whilst using Parallels in Coherence mode I can use Windows programs alongside MAC apps so don’t need to duplicate MS Office installations.