I am right-clicking on an .mrimg (Macrium Reflect) image file, then clicking menu item "explore image", and is getting error message "Macrium Reflect - Failed to access". I have DOpus beta 12.3.7. In Windows Explorer, I have one right-click bold "explore image" menu item, which results in the same error message, and one non-bold "Explore image" menu item, which shows thecontents of the .mrimg file. It does not matter if the drive is mounted or not.
It must be Macrium Reflect problem. I'm using MR v6 free and everything works in DO and in Explorer - just one "Explore Image" item in menu. So my guessing is that:
You're recently upgraded v6 to v7, which may not change proper registry entries (I saw that last v6 update and it has this in changelog: "This release improves on the previous release v6 to v7 upgrade experience by allowing v7 upgrade keys to automatically upgrade existing v6 keys").
You have two separate Macrium services. How and why? I don't know, but there must be some services or registry entries conflict so your computer trying to access Macrium Reflect images with wrong, not existing version of program.
I had not upgraded to v7 before, because I had forgotten about its announcement. So, I uninstalled v6 altogether, cleaning up a little manually and then installed v7. After replacing Windows Explorer by DOpus, then restarting the PC, I check and there was no Explore Images in the DOpus right-click menu. However, when I double-clicked on a .mrimg file, it opened nicely (as it had not too long ago, before my troubles), and everything was, and is, honky dory.
By the way, I probably had two separate Macrium Reflect services (as you suggested). Remember, I had two "Explore Images" in WE, one working and the other not, and perhaps DOpus 'inherited' the non-working one.